People here think they're computers, when repeated double blind tests have proven even audio professionals can't tell a 160bit properly encoded LAME mp3 and a 320 FLAC apart.
But yes, YOU'RE the exception right?
160 and FLAC I can do, with good equipment. (I've done it before, and on my own equipment. New standardized environment, maybe not.)
At 256 Kbps MP3 and FLAC.. I can't tell.