NVIDIA has a new driver ready and waiting for you guys. It's build revision 180.84 and comes in beta form.
According to our forum thread on this driver is has several improvements for Grand Theft Auto 4. If you give these a try, let us know how they work out.
The drivers come with the PhysX 8.10.13 system software as well.
Supported cards are (and there are a whole bunch of them):
Have you checked out Guru3D's Left 4 Dead Graphics performance article already ?