HD5850 OC

So.. finally got a nice new cooler on my HD5850. Zalman VF3000. Works like a charm. Idle It still sits high mainly due to my case being rather cramped and what not.. But currently pushing 900/1200, I max out around 60-65 degrees on GPU, and about 70 on the VDDC. That's with 1.2 volts. (Furmark 10mins)

Now I have a question.. I'm using MSI Afterburner. I notice when you apply something via afterburner, you cannot then set it to its 'idle' mode where it would be cooler and use less voltage.. Is there a way to keep this 'cool n quiet' mode after changing the clock/voltage settings in afterburner?

Also, with that said, how far do you reckon I could/should push my GPU? I'm sure I could use less voltage for my current 900 core, but I'm thinking of going up more..

Self bump + update...

Turns out I'm not stable at 900/1200.. I downclocked the memory to 1100, and I'm still not stable... I even pumped up the voltage in MSI Afterburner to like 1.3 just to test.. No dice. Did I get a bad GPU? Or am I doing something wrong?