I have found that if I listen really close, I can hear slight differences between the uncompressed original and the aac@160 - but I have to really focus on specific small pieces of the sound. At 128 the differences are fairly apparent (as it is with mp3@160).
Different sets of ears will have different cut-offs, as will different peoples' psychologies. See what bit rate works well for your ears, and go with it. It doesn't take long to rip a song at several different bit rates. See if you can really tell a significant difference between 128 and 160, or even 96 or 192. Your opinion is the only one that really matters. There will be other folks whose ears are more finely tuned than yours; and a larger number who think theirs is - but you're not ripping for them.