Hi Desudeus - I have used the GTX-660-Ti on 10.8.3 and it worked great on some of my larger models (130mb+) It starts of a little sluggish but once it has done a few rotations it becomes smoother but you certainly don't get too much of a speed boost. Sadly I am back on Windows at the moment so can't give you a frame rate, but If i remember rightly on default MoI interface settings I got 15.?? fps on my Lamborghini model that can be found on the forum here http://moi3d.com/forum/index.php?webtag=MOI&msg=5101.1 ... Once i have mastered some poly modelling application then i will be returning to Mountain Lion - It's so much smoother on rendering and working on other things.

Other specs that might have some influence ...

CPU i3570k @ 3.8ghz quad core but no HT
32gb 1600Mhz
GTX660ti
SATA-II Drives @ 1TB and 500 Gbytes

To be honest, I am a little disappointed with the bang per buck of the 660ti, but I use Keyshot for rendering which is CPU based and not GPU based, however Blender Cycles gets a massive boost over the old 560 I was using. I have gotr round to setting things in Modo to use GPU, or indeed if Modo can use it, but the render engine in Modo is pretty damn rapid too

Hope that helps you a little ...

Martin Spencer-Ford