Indeed 320 KBits/sec does the trick for me
Several years ago, I took a track from a Decemberists CD, encoded it at 64Kbits, 128Kbits, 256 KBits, 320 Kbits, both MP3 and AAC, along with the original song's bits, and then made a new CD with the resulting songs. Played it on my decent component stereo (probably cost about $2000 in today's USD). 64Kbits definitely sounded flat, and I thought that 128 was still perceptibly worse than lossless. Both 256 Kbits and 320 Kbits were indistinguishable to me from the original CD. So, I've been happy with 320Kbits rips since then; 256 would probably be fine, but I figured a little extra wouldn't hurt.
Actually, I did a few other things as well -- some classical piece I've forgotten, and something from Phillip Glass. All basically behaved the same as the Decemberists.
With regard to MP3 or AAC, I really couldn't tell any difference once I got to 256 Kbits or above.