Stock: I'm at 771/1944/1062 on my GTS-512 at 100% fan stable for at least 25mins in ATI Tool, and made it through 8 loops of Battle of Proxycon (3DMark03). I consider this stable.

16190-3DMArk06 w/ 450x8 (3.6GHz) x3210 Quad, P5K-Premium, 2GB RAM @ 1125MHz 5-5-4-10 --> (24/7 stable).

I haven't tried to test for stability at lower fan settings yet.