Re: Tweaks for KDE4 ?
Kwin in KDE4 is a lot more integrated unlike Compiz is in GNOME, since it's not the window manger for the DE, distros just make it so. It wasn't too long ago people complained about Compiz performance issues with NVIDIA too.
I'm not sure if they fixed the Oxygen deco bug that hurt performance. Try a different window decoration than the default Oxygen one.