Yeah, my advice would be: rip something you really love, really know well, that has intricate sonic details, at 128k AAC. Play it in the best case scenario -- find a quiet room, maybe hook up to your stereo and turn it up, or use the nicest over-ear headphones available. If you're happy, stick with that. If not, try cranking up the bit rate. If you can't get happy that way, try lossless next....
It really varies between people. Also there's a difference between music lovers and audiophiles -- that is, most audiophiles love music, but not everyone needs 100% optimal clarity to really enjoy music. I was trained in violin for nine years, and I love a wide variety of music, but to be honest, 128 AAC works for me almost always, because the way my mind works, it is happy enough to fill in the blanks -- I can tell the difference between it and the CD, but I adjust to it and it doesn't bother me much. After a while, I can only notice the differences if I listen very, very closely. But that's *ME*. Other people cannot easily make themselves stop noticing.