In CentOS 6.3 x86 with 304.xx drivers 2d rendering speed is abysmal - scrolling of any web page in Firefox 16 web browser causes 100% CPU usage.
Another problem is when you launch any OpenGL application, you cannot do anything else - screen dragging around the desktop becomes jerky and very slow.
I’m NOT using any composite window manager and I have all special effects totally disabled.
It is all a matter of nvidia not supporting server side gradient acceleration. The patch i talked about in the link is just a workaround that make things more efficient by relying on the cpu.
But this also means that all of the drivers that accelerates it in hardware will be penalized.
That’s why archlinux devs removed that patch from cairo package, and unfortunately they’re doing it right; nouveau really shines without the patch.
Wourkaround:
If you don’t want to mess things with code patching, just choose a (VERY) basic gtk theme.