You should be able to get it to 900 no problem. Just bump it up by ten and play BF3 for 10 mins. You'll know its unstable when there is artifacts, screen glitches, etc. Just don't go crazy and set something like 1000 Mhz to start.
Yeah, I don't have money for BF3, so I'll definitely be using 3DMark11, only demanding game I'll be playing is Tribes: Ascend, and that's because it's free. Will literally have nothing for games after I buy this.