Create a frequency spectrogram of your PCM files. If the max. shown frequency is e.g. 11025Hz, load your PCM file with a samplerate of 22050Hz, etc.
I started with an original which is 8bit, mono, 16Khz. (What i believe the OP's file is).I've imported the file with the three alternative settings that we've talked in this thread (the one the OP has found to fit his options, and two more of mine).All four files seem to play well (at least at the appropiate speed). But it is obvious that the lower the sampling rate, the worse it sounds.