Anything higher than 128 Kbps would be a waste from YouTube. There isn't even that much quality to begin with.
To explain olyteddy's comment... You can't improve the quality of anything by changing the format. Teddy was a bit generous I bet 90 CBR is way high for Youtube. That is why the music industry doesn't mind Youtube. The music is garbage quality. It is free and legal but probably 70 CBR the same as FM radio, HD radio is 90. Saving it to 320 CBR will not recover all the lost music info that was removed when it was compressed to 70 BR. It will only make the file much larger.