Interesting. I did some tests with my own RMS tool (nicknamed K20RMS currently as it uses the K-System and K-20 headroom but with a Z weighting "flat filter" aka plain RMS).
Using the same test suit as R128 http://r128gain.sourceforge.net/
I get the following:
K20RMS v1.0
E:\Downloads\Audio\audio tests\ebu-loudness-test-setv01\1kHz Sine -20 LUFS-16bit.wav
Within 1dB (+/- 0.5dB) and peak is 0.0 dBFS or less.
Gain adjustment is not advised in this case.
Title RMS: -19.93 dBFS (0.1008560, 83.07 dBSPL)
Title Peak: -19.94 dBFS (0.1007385)
Title Dynamic Range: 0.03 dB (max RMS -19.91 dBFS, min RMS -19.94 dBFS)
Title Dynamic Headroom: -0.01 dB (0.9988354)
Title Dynamic Energy: 0.02 dB (1.0019993)
Title Gain ref -20dBFS/83dBSPL: -0.07 dB (0.9915128)
Title Modifier: -0.07 dB (0.9915128)
Title Final Peak: -20.01 dBFS (0.0998835)
Title Final RMS: -20.00 dBFS (0.1000000, 83.00 dBSPL)
E:\Downloads\Audio\audio tests\ebu-loudness-test-setv01\1kHz Sine -26 LUFS-16bit.wav
Title RMS: -25.90 dBFS (0.0506862, 77.10 dBSPL)
Title Peak: -25.93 dBFS (0.0505066)
Title Dynamic Range: 0.04 dB (max RMS -25.88 dBFS, min RMS -25.93 dBFS)
Title Dynamic Headroom: -0.03 dB (0.9964557)
Title Dynamic Energy: 0.02 dB (1.0024331)
Title Gain ref -20dBFS/83dBSPL: 5.90 dB (1.9729222)
Title Modifier: 5.90 dB (1.9729222)
Title Final Peak: -20.03 dBFS (0.0996456)
Title Final RMS: -20.00 dBFS (0.1000000, 83.00 dBSPL)
E:\Downloads\Audio\audio tests\ebu-loudness-test-setv01\1kHz Sine -40 LUFS-16bit.wav
Title RMS: -39.96 dBFS (0.0100410, 63.04 dBSPL)
Title Peak: -39.78 dBFS (0.0102539)
Title Dynamic Range: 0.03 dB (max RMS -39.95 dBFS, min RMS -39.98 dBFS)
Title Dynamic Headroom: 0.18 dB (1.0212016)
Title Dynamic Energy: 0.02 dB (1.0020251)
Title Gain ref -20dBFS/83dBSPL: 19.96 dB (9.9591475)
Title Modifier: 19.96 dB (9.9591475)
Title Final Peak: -19.82 dBFS (0.1021202)
Title Final RMS: -20.00 dBFS (0.1000000, 83.00 dBSPL)
E:\Downloads\Audio\audio tests\ebu-loudness-test-setv01\seq-3341-1-16bit.wav
Title RMS: -22.91 dBFS (0.0714933, 80.09 dBSPL)
Title Peak: -22.94 dBFS (0.0713196)
Title Dynamic Range: 0.03 dB (max RMS -22.90 dBFS, min RMS -22.93 dBFS)
Title Dynamic Headroom: -0.02 dB (0.9975703)
Title Dynamic Energy: 0.01 dB (1.0016830)
Title Gain ref -20dBFS/83dBSPL: 2.91 dB (1.3987327)
Title Modifier: 2.91 dB (1.3987327)
Title Final Peak: -20.02 dBFS (0.0997570)
Title Final RMS: -20.00 dBFS (0.1000000, 83.00 dBSPL)
E:\Downloads\Audio\audio tests\ebu-loudness-test-setv01\seq-3341-2-16bit.wav
Title RMS: -32.94 dBFS (0.0225409, 70.06 dBSPL)
Title Peak: -32.75 dBFS (0.0230408)
Title Dynamic Range: 0.03 dB (max RMS -32.93 dBFS, min RMS -32.95 dBFS)
Title Dynamic Headroom: 0.19 dB (1.0221772)
Title Dynamic Energy: 0.01 dB (1.0015823)
Title Gain ref -20dBFS/83dBSPL: 12.94 dB (4.4363842)
Title Modifier: 12.94 dB (4.4363842)
Title Final Peak: -19.81 dBFS (0.1022177)
Title Final RMS: -20.00 dBFS (0.1000000, 83.00 dBSPL)
E:\Downloads\Audio\audio tests\ebu-loudness-test-setv01\seq-3341-3-16bit.wav
Title RMS: -27.53 dBFS (0.0420017, 75.47 dBSPL)
Title Peak: -22.92 dBFS (0.0714722)
Title Dynamic Range: 17.08 dB (max RMS -22.91 dBFS, min RMS -39.99 dBFS)
Title Dynamic Headroom: 4.62 dB (1.7016501)
Title Dynamic Energy: 4.62 dB (1.7021379)
Title Gain ref -20dBFS/83dBSPL: 7.53 dB (2.3808570)
Title Modifier: 7.53 dB (2.3808570)
Title Final Peak: -15.38 dBFS (0.1701650)
Title Final RMS: -20.00 dBFS (0.1000000, 83.00 dBSPL)
E:\Downloads\Audio\audio tests\ebu-loudness-test-setv01\seq-3341-4-16bit.wav
Title RMS: -29.63 dBFS (0.0329802, 73.37 dBSPL)
Title Peak: -23.00 dBFS (0.0708008)
Title Dynamic Range: 51.77 dB (max RMS -22.82 dBFS, min RMS -74.58 dBFS)
Title Dynamic Headroom: 6.64 dB (2.1467686)
Title Dynamic Energy: 6.82 dB (2.1926796)
Title Gain ref -20dBFS/83dBSPL: 9.63 dB (3.0321255)
Title Modifier: 9.63 dB (3.0321255)
Title Final Peak: -13.36 dBFS (0.2146769)
Title Final RMS: -20.00 dBFS (0.1000000, 83.00 dBSPL)
E:\Downloads\Audio\audio tests\ebu-loudness-test-setv01\seq-3341-5-16bit.wav
Title RMS: -22.94 dBFS (0.0713034, 80.06 dBSPL)
Title Peak: -19.93 dBFS (0.1008301)
Title Dynamic Range: 6.03 dB (max RMS -19.92 dBFS, min RMS -25.95 dBFS)
Title Dynamic Headroom: 3.01 dB (1.4140999)
Title Dynamic Energy: 3.02 dB (1.4154997)
Title Gain ref -20dBFS/83dBSPL: 2.94 dB (1.4024584)
Title Modifier: 2.94 dB (1.4024584)
Title Final Peak: -16.99 dBFS (0.1414100)
Title Final RMS: -20.00 dBFS (0.1000000, 83.00 dBSPL)
E:\Downloads\Audio\audio tests\ebu-loudness-test-setv01\seq-3341-6-5channels-16bit.wav
Title RMS: -27.19 dBFS (0.0436962, 75.81 dBSPL)
Title Peak: -24.00 dBFS (0.0630798)
Title Dynamic Range: 0.00 dB (max RMS -27.19 dBFS, min RMS -27.19 dBFS)
Title Dynamic Headroom: 3.19 dB (1.4435992)
Title Dynamic Energy: 0.00 dB (1.0000000)
Title Gain ref -20dBFS/83dBSPL: 7.19 dB (2.2885273)
Title Modifier: 7.19 dB (2.2885273)
Title Final Peak: -16.81 dBFS (0.1443599)
Title Final RMS: -20.00 dBFS (0.1000000, 83.00 dBSPL)
E:\Downloads\Audio\audio tests\ebu-loudness-test-setv01\seq-3341-6-6channels-WAVEEX-16bit.wav
Title RMS: -27.19 dBFS (0.0436962, 75.81 dBSPL)
Title Peak: -24.00 dBFS (0.0630798)
Title Dynamic Range: 0.00 dB (max RMS -27.19 dBFS, min RMS -27.19 dBFS)
Title Dynamic Headroom: 3.19 dB (1.4435992)
Title Dynamic Energy: 0.00 dB (1.0000000)
Title Gain ref -20dBFS/83dBSPL: 7.19 dB (2.2885273)
Title Modifier: 7.19 dB (2.2885273)
Title Final Peak: -16.81 dBFS (0.1443599)
Title Final RMS: -20.00 dBFS (0.1000000, 83.00 dBSPL)
E:\Downloads\Audio\audio tests\ebu-loudness-test-setv01\seq-3341-7_seq-3342-5-24bit.wav
Title RMS: -22.59 dBFS (0.0742564, 80.41 dBSPL)
Title Peak: -8.91 dBFS (0.3583316)
Title Dynamic Range: 13.72 dB (max RMS -16.88 dBFS, min RMS -30.60 dBFS)
Title Dynamic Headroom: 13.67 dB (4.8255968)
Title Dynamic Energy: 5.70 dB (1.9282742)
Title Gain ref -20dBFS/83dBSPL: 2.59 dB (1.3466849)
Title Modifier: 2.59 dB (1.3466849)
Title Final Peak: -6.33 dBFS (0.4825597)
Title Final RMS: -20.00 dBFS (0.1000000, 83.00 dBSPL)
E:\Downloads\Audio\audio tests\ebu-loudness-test-setv01\seq-3341-8_seq-3342-6-24bit.wav
Clipping caused by the gain, modifier was adjusted to protect peaks,
volume will be lower than expected.
Title RMS: -23.90 dBFS (0.0638479, 79.10 dBSPL)
Title Peak: -2.87 dBFS (0.7182941)
Title Dynamic Range: 31.36 dB (max RMS -11.96 dBFS, min RMS -43.31 dBFS)
Title Dynamic Headroom: 21.02 dB (11.2500906)
Title Dynamic Energy: 11.94 dB (3.9531405)
Title Gain ref -20dBFS/83dBSPL: 3.90 dB (1.5662234)
Title Modifier: 2.87 dB (1.3921874)
Title Final Peak: 0.00 dBFS (1.0000000)
Title Final RMS: -21.02 dBFS (0.0888882, 81.98 dBSPL)
E:\Downloads\Audio\audio tests\ebu-loudness-test-setv01\seq-3342-1-16bit.wav
Title RMS: -22.41 dBFS (0.0757570, 80.59 dBSPL)
Title Peak: -20.00 dBFS (0.1000061)
Title Dynamic Range: 10.00 dB (max RMS -19.82 dBFS, min RMS -29.82 dBFS)
Title Dynamic Headroom: 2.41 dB (1.3200905)
Title Dynamic Energy: 2.60 dB (1.3484154)
Title Gain ref -20dBFS/83dBSPL: 2.41 dB (1.3200099)
Title Modifier: 2.41 dB (1.3200099)
Title Final Peak: -17.59 dBFS (0.1320090)
Title Final RMS: -20.00 dBFS (0.1000000, 83.00 dBSPL)
E:\Downloads\Audio\audio tests\ebu-loudness-test-setv01\seq-3342-2-16bit.wav
Title RMS: -16.63 dBFS (0.1473578, 86.37 dBSPL)
Title Peak: -15.00 dBFS (0.1778259)
Title Dynamic Range: 5.00 dB (max RMS -14.82 dBFS, min RMS -19.82 dBFS)
Title Dynamic Headroom: 1.63 dB (1.2067628)
Title Dynamic Energy: 1.82 dB (1.2326562)
Title Gain ref -20dBFS/83dBSPL: -3.37 dB (0.6786202)
Title Modifier: -3.37 dB (0.6786202)
Title Final Peak: -18.37 dBFS (0.1206763)
Title Final RMS: -20.00 dBFS (0.1000000, 83.00 dBSPL)
E:\Downloads\Audio\audio tests\ebu-loudness-test-setv01\seq-3342-3-16bit.wav
Title RMS: -22.78 dBFS (0.0725930, 80.22 dBSPL)
Title Peak: -20.00 dBFS (0.1000061)
Title Dynamic Range: 20.00 dB (max RMS -19.82 dBFS, min RMS -39.81 dBFS)
Title Dynamic Headroom: 2.78 dB (1.3776278)
Title Dynamic Energy: 2.97 dB (1.4071872)
Title Gain ref -20dBFS/83dBSPL: 2.78 dB (1.3775438)
Title Modifier: 2.78 dB (1.3775438)
Title Final Peak: -17.22 dBFS (0.1377628)
Title Final RMS: -20.00 dBFS (0.1000000, 83.00 dBSPL)
E:\Downloads\Audio\audio tests\ebu-loudness-test-setv01\seq-3342-4-16bit.wav
Title RMS: -26.53 dBFS (0.0471508, 76.47 dBSPL)
Title Peak: -20.00 dBFS (0.1000061)
Title Dynamic Range: 29.99 dB (max RMS -19.82 dBFS, min RMS -49.80 dBFS)
Title Dynamic Headroom: 6.53 dB (2.1209822)
Title Dynamic Energy: 6.72 dB (2.1664915)
Title Gain ref -20dBFS/83dBSPL: 6.53 dB (2.1208527)
Title Modifier: 6.53 dB (2.1208527)
Title Final Peak: -13.47 dBFS (0.2120982)
Title Final RMS: -20.00 dBFS (0.1000000, 83.00 dBSPL)
Clipping caused by gain, modifier adjusted to protect peaks.
Album RMS: -23.69 dBFS (0.0654086, 79.31 dBSPL)
Album Peak: -2.87 dBFS (0.7182941)
Album Dynamic Range: 62.62 dB (max -11.96 dBFS, min -74.58 dBFS)
Album Dynamic Headroom: 20.81 dB (10.9816437)
Album Dynamic Energy: 11.73 dB (3.8588116)
Album Gain ref -20dBFS: 3.69 dB (1.5288506)
Album Modifier: 2.87 dB (1.3921874)
Album Final Peak: 0.00 dBFS (1.0000000)
Album Final RMS: -20.81 dBFS (0.0910610, 82.19 dBSPL)
As you can see R128 is much closer to RMS, and if you run the test suit through ReplayGain (foobar2000) you can see that RG89 is a tad more inconsistent, so R128 is looking pretty good so far.