in terms of "could I pass an ABX test with a good score": not even close
in terms of "does some music probably sound a bit better to me straight from the CD for various reasons": yes
for a portable player, I always stick to 320k or lower, mostly because of space (I'd rather have a ton of music at good quality, than a bit of music at insane quality (that isn't really noticably better anyways))
you might also wanna consider the codec package being used:
Windows Media Audio - Wikipedia, the free encyclopedia
WMA usually performs better with lossier compression (contrasted to mp3 and whatnot, ATRAC is probably a bit better, but lets not go there)