I can't really say anything about the relative sound quality, but there's something I've been wanting to bring up for a while now: you're encoding these audio files at a rather high bitrate.128 kilobit per second is appropriate when encoding professionally produced music, ripped from a CD, but it's almost ridiculously high for a recording of speech, captured with an ordinary microphone on a home computer. You could probably go as low as 64 kb/s without any loss of quality discernible with the human ear - especially if you used a 2-pass, variable-bitrate encoding with 64 kb/s as the target average.
Just out of curiosity, what software do you use for capturing, post-processing and encoding?