did some testing of my own with GrieverV's aggressively optimized Skylake 1d5299d 1.3.3 flac.exe. I don't use -ep so I left it out and compared it to my up until recently used flac 1.3.2 (official xiph generic windows binary, flac-1.3.2-win.zip). SSD to SSD, i7-7700K, it's 25 % faster! (I know, apples and oranges, but I switched from this 1.3.2 to GrieverV's 1.3.3 just now and I'm gonna stick with it, so this is my real life improvement)
PS C:\Program Files (x86)\foobar2000\Encoders\skylakeflac> Measure-Command { ..\flac.exe --verify --best E:\flac_reenc_AIO\Image.wav -o E:\flac_reenc_AIO\Image_new.flac }
flac 1.3.2
Copyright (C) 2000-2009 Josh Coalson, 2011-2016 Xiph.Org Foundation
flac comes with ABSOLUTELY NO WARRANTY. This is free software, and you are
welcome to redistribute it under certain conditions. Type `flac' for details.
Image.wav: Verify OK, wrote 2816137583 bytes, ratio=0,789
Days : 0
Hours : 0
Minutes : 1
Seconds : 50
Milliseconds : 85
Ticks : 1100852308
TotalDays : 0,00127413461574074
TotalHours : 0,0305792307777778
TotalMinutes : 1,83475384666667
TotalSeconds : 110,0852308
TotalMilliseconds : 110085,2308
PS C:\Program Files (x86)\foobar2000\Encoders\skylakeflac> Measure-Command { .\flac_1d5299d_skylake_2020-03-25.exe --verify --best E:\flac_reenc_AIO\Image.wav -o E:\flac_reenc_AIO\Image_new.flac }
flac 1.3.3
Copyright (C) 2000-2009 Josh Coalson, 2011-2016 Xiph.Org Foundation
flac comes with ABSOLUTELY NO WARRANTY. This is free software, and you are
welcome to redistribute it under certain conditions. Type `flac' for details.
Image.wav: Verify OK, wrote 2816138302 bytes, ratio=0,789
Days : 0
Hours : 0
Minutes : 1
Seconds : 23
Milliseconds : 653
Ticks : 836538482
TotalDays : 0,000968215835648148
TotalHours : 0,0232371800555556
TotalMinutes : 1,39423080333333
TotalSeconds : 83,6538482
TotalMilliseconds : 83653,8482