Drivers run quite well in Grid. I'll have to install some games that actually use more complex physics, but Warmonger is running quite well and also, for all those old gamers, Alien Vs Predator 2 works very well. Good 3DMark06 performance and good IQ. I'll post some benchmarks after I've installed a couple games.
I think Grid does have flags and stuff that blow in the wind and I would assume physics drivers would help that, though I don't think the physics in grid are overly complex.
Upgrading physx drivers can improve performance in some games and it may help a little with Grid. Though it may slow down frame rates in games that use complicated physics if you have the physics settings set at high settings. I'm going to install Company of Heroes to see how these work with that game and the different physics settings.