Just throwing my 2¢ into the 320 vs Flac.
For reference, I use dbAudioconveter which is an $80 audio converter with the most up-to-date mp3 lame conversion.
Now the problem is, people have no idea what they're listening for on 320 vs flac. Listen to some 8kbps, 16, 32, and so on until you get to 320kbps then try flac, see if you hear the same difference.
Anyway, some of the problems with flac vs. 320 is that mediocre encoders and false 320kbps are everywhere. Meaning that. 256kbps can be converted to 320kbps without any improvement and be touted as a better version. The real way to do it is convert it yourself from Flac to 320kbps and see if you hear a difference.
Another reason some flac sound better is because of what I referenced earlier, 320 coming from a 256 rather than a flac file. Generally CDs are mastered better/differently than their 256kbps counterparts so with that in mind, I always buy the CD, convert it to ALAC for iTunes compatibility & 320kbps for mobile use. This is the best set up for me.