When OCing, what's the best way to check stability?

When OCing a GPU, what's the best way to check for problems/artifacts?

I'm wondering because ATITool found a max core of 575MHz and 615MHz memory on my X850XT using Omega drivers. Those numbers are way over the stock 520MHz and 540MHz numbers.

I was thinking about letting I have the full version of 3DMark 06 if that's got some stress tests that I could use.

I ran 3DMark 05 and 06 one right after another and the temps never hit above 67C.

Seems fairly stable at 558.9 core and 618 memory. I'll have to try those loop tests you guys mentioned though to see if it really is stable.

My max temps with ATITool was 66C GPU, 68C environment. I did both the 3D view for 10 minutes and artifact checks for 35 minutes when OCed (560 & 615).

With Catalyst, my OCs are not as good. I got 540 max core and have my memory at 560 (not maxed yet). But at stock speeds, my benchs are a bit better using Catalyst drivers.