Yeah the BIOS is always the way to go. Windows OC programs are pretty inaccurate as rbstr said. I use ClockGen pretty much just for referance. A good program to have is CPU-Z, which gives you great info on your CPU and RAM settings.
ASUS BIOSes rock. There are times I wish my Shuttle AN50R had the flexibility of those BIOSes. I check the Shuttle website weekly for new BIOSes to flash up to (the first BIOS that came with my card had almost NO OCing features). So far I've had to flash my BIOS twice just to get CPU multipliers and RAM timings in my BIOS.
