On the most recent drivers, it works for all versions and all GPUs. I have a 550 Ti and it works great. I think I'm using 301.42 and it works fine with that version. Just enable it under 3d settings in the nVidia control panel.
Desktop:
OS: Windows 7 64 bit
CPU: Intel Core i5 3570K @ 4.4 GHz
GPU: EVGA NVIDIA GeForce GTX 550 Ti (Factory OC'ed)
RAM: 16 GB @ 1600 MHz
Dolphin Revision:3.0, 3.0-784, 3.5, latest 3.5
OS: Windows 7 64 bit
CPU: Intel Core i5 3570K @ 4.4 GHz
GPU: EVGA NVIDIA GeForce GTX 550 Ti (Factory OC'ed)
RAM: 16 GB @ 1600 MHz
Dolphin Revision:3.0, 3.0-784, 3.5, latest 3.5