Hmmm, honestly I haven't upgraded because I'm quite satisfied with my current setup.

Villain ROM
- Samsung TouchWizz base (Camera works properly and MOD'ed Multi-Window)
- AOKP customization features
- Some innovations from Samsung (the Phone/Contacts, and SMS are good, the browser's not half bad)
- Still using Apex PRO, and no custom lockscreen (I've got a pw)

...there's some lag at times (not scrolling or swiping, just when tapping to open certain things), but nothing unbearable