8600 GTS GPU is clearly bottlenecking the whole system, resulting in lower fps than even a GTX 580, despite the fact that if single NVIDIA GPU is used in Mafia II, PhysX effects are partially running on CPU.
|GTX 580 + 8600 GTS||30.3 fps|
|GTX 580||49.7 fps|
|GTX 580 + GTX 580||57.5 fps|
|GTX 580 + GTX 550 Ti||56.6 fps|
|GTX 580 + GTX 560 Ti||55.3 fps|
In conclusion, in case if you want to pair a dedicated PhysX card with GTX 580-class GPU, find a decent one – GTX 550 or “even something a little bit lower-end”, as author of this video recommends.