I am running 3 machines (desktops) with NVidias: : GT9500 and GT9600 (dead slow, unusable, but no compiz crashes) and one with GTS450 (slow, but usable, because the VGA Card is much more powerful, no compiz crashes). I have just tested NVidia 295.20 and have the same problem. All desktops are powerful ones: AMD Phenom II X6, 6-cores, @3.4GHz, 16GB Ram. I have never seen they running slow, no matter the load.
I have also noticed one new thing: All cads are running hotter than normal (I noticed the fan noises). They can't move from "performance mode" to "adaptive mode". It's like if they all PCs were running something very heavy. But they are not.