Anecdotal, but... I've been a musician for 36 years and have fantastic hearing not just for my age but for any age. I know, I have to get it quantitatively tested twice a year!

I can't tell the difference at all between FLAC and 320 kbps from the same source. I can tell a difference between FLAC and 128 kbps, but it's not huge. It sounds a bit dull, but I have to be looking for the difference and comparing the two. If you just gave me one or the other with no reference, I might suspect the 128 if it was a simple recording of a single instrument or a song I'm intimately familiar with, and even then I wouldn't be sure of it. It just sometimes "feels" weird.

So I converted over 4 terabytes of my music stash to 320 kbps and cut the total space into less than 2. Feels good.