I experienced the same problems with a new install of OpenSuse 12.1 and nvidia driver 295.20 64bit.
What solved it for me, was to change the PowerMizer settings of the GPU. This can be done via nvidia-settings tool (change PowerMizer Preferred Mode to: Prefer Maximum Performance). This will not be sticky, so you will have to do that after each login to your DE.
You can also permanently change it in your /etc/X11/xorg.conf file:
BoardName "GeForce GTX 560 Ti 2048MB"
Option "RegistryDwords" "PowerMizerEnable=0x1; PerfLevelSrc=0x2222; PowerMizerDefault=0x2; PowerMizerDefaultAC=0x2"
There are at least three performance modes you can set this way. This one is the middle one, which does the trick for me.
I found this piece of information on this site, more explanations there: