I did a comparison of the same song from a cd ripped at 96, 128, 160, 192, 256, and 320 kps.
I noticed a significant reduction in sound quality going from the cd to 160 kps or below.
I noticed a slight to moderate reduction in sound quality going from the cd to 192 or 256 kps.
I thought the sound quality of the cd and the song ripped at 320 kps was close. I suspect this is somwhat dependent on the song.
This was done in a fairly quiet room using a two satelite and two 12" sub-woofer speaker system driven by an 100 watt\ch Sony receiver. This systeim is not true audiophile quality where a speaker system can costs $10,0000. But it is better than the best self powered computer speaker system I have heard.
In my car, it seems to me that a song ripped at 128 kps sounds better than the best FM reception I have gotten.