TL;DR - Heaven says 1106mv is stable for 30 minutes with 1175mhz, Crysis 1 and 2 combined say 1150mhz isn't even stable at 1162mv (still testing). Is this normal?
I got one 3 days ago and it's been a messy time overclocking. Instability = driver crash and the only fix is a driver reinstall.
30 minutes of Heaven said 1106mv 1175mhz was stable without artifacts. Unfortunately 1.2ghz didn't come even with 1200mv. Many runs of heaven, 3dmark11, Crysis 1 says memory is stable to at least 1800mhz, with steady gains in fps - it's at 1600mhz right now.
Unfortunately, Crysis 2 revealed in 1 minute that Heaven was inaccurate about core, and after going through lots of reinstalls and reruns, even 1200mv didn't yield 1175mhz. I went down to 1150mhz, and tried at 1106, 1112, 1125, 1149mv - all with problems before 30 minutes (one tree has this one spot that flashes red or green a little when my oc is unstable, and it doesn't do it at stock). On a particularly unstable overclock below 1125mv, there's one doorframe that flashes white checkerboards.
Now testing with Crysis 1 benchmark tool, and 1143mv showed an artifact within 1 run. 1149mv showed an artifact 11 runs in, 1156mv - 35 runs in, 1162mv - 22 runs, 1168mv - 25 runs. Now testing 1174mv at 1150mhz with the aim of no artifacts by 55 runs (30 minutes). This artifact is like the one in Crysis 2 - just one specific tree, with one tiny patch that flashes red or green for one frame as the benchmark passes it. With 1181mv, this flash isn't there, at stock clocks this flash isn't there. So it's definitely a hardware artifact... meaning 1150mhz takes between 1174mv and 1181mv.
Is this normal - like, heaven being fine at 1106mv 1175mhz but crysis/crysis 2 taking a hell of a lot more for a smaller overclock?
it seems you are trying too much to get every last drop of performance out of your card, ocing wont get you usually more than 5ish fps increase, reduce the OC to 10-20% and you should be fine, i recommend to not touch the voltage either because thatll kill the card if you put too much. as for your questions yes heaven is a benchmarking program designed to benchmark and crysis/crysis 2 is just a game but people use it to benchmark. just reduce the overclock, you dont need to be stressing over 1-2 fps really, its not worth it.