Low performance with PhysX probably isn't a bug, PhysX is just all-around poorly implemented.
I've also heard of poor FPS when V-Sync is turned on, which would hopefully be fixed by the time the game's released.
Grabbing the demo now though, so we'll see how yesteryear's high-end hardware holds up, but from what I've seen so far everything is peachy besides PhysX.
Edit- Yep, Vsync absolutely murders my performance, which is otherwise pretty good, even with APEX set to high I get around 25ish, which is more than I was expecting considering they recommended my main GPU as just dedicated PhysX. :rolleyes: I may grab a used 8800 GT for PhysX though, because it actually looks pretty good in this game.
Aside from that, once you change the driving mode from that horrid, ultra-responsive arcade mode to Simulation, the gameplay is near perfect IMO. I can easily see this becoming my GOTY just as I expected it to.