http://www.youtube.com/watch?v=ik-me8RWEWc, the effects are really nice looking even on medium. It honestly does take something along the lines of a GTX 480 w/ 285 PhysX for decent FPS at a high resolution and PhysX on high. A big hit is clothing though. A lot of folks disable cloth PhysX for every NPC, leaving only Vito with dynamic clothing and about a 15-30 FPS boost.
I can attest to this, I have every setting maxed out, and PhysX on High but only for particle effects and Vito's clothing and it runs like a dream.