Perhaps there is a scaling issue for SLI users or Wand3r is using an outside configuration to push his system further?
On my end, I can vouch for Keys. My GF's rig isn't as elaborate as other's and the lowest we've seen her system go to was 47 FPS. It's possible it went lower, but she hasn't mentioned it.
Hybrid PhysX isn't a cure all either, there are instances where my system has sporadoic stops as if something is loading. It would make the game unplayable, however, the GTX 680 system experiences no issues or slow downs as severe.
Either way, the PhysX effects are a great addition in this game. Sure you don't need them, but after playing the game with them I wouldn't want to play without them. Kudos nVidia on adding something of value, for once