Actually, I take that back. My overclocks on air was my completely stable overclock. Lower temps don't mean much for overclocking the GTX 680's. However, I find it odd that I can be stable at some games and benchmarks with higher overclocks that aren't stable for others.
I got my temps up to 45C after some Metro 2033.
Yea it's odd. On my 570, I can hit 1000mhz and Heaven/OCCT and gaming is great, but 3DMark11 craps out after a minute or two. Lowering to 975core makes everything ok. *shrugs*