I have overclocked my GTX 560ti to 950mhz core and 2250mhz memory, using CPC's latest article on overclocking. I have not experienced any artifacting or glitches during my run of unigine heaven, it was running for a couple of hours, and i gained about 6fps. Is it a good idea to try pushing it any further? I'm not really getting any temps higher than 60C on load.
If the temps are stable I'd say go higher, but play it safer from now on and rise in smaller gains. You should be able to get some more power off her yet (though keep an eye out for glitches and high temperatures). Looks like you may have a prime card there...
I hope so. I know all cards are different overclocking wise. I just don't want to push it too far as to damage it.