Right now it idles at about 38-41 C and when I really tax it, the temps will hit about 49-53 C.
You have some room there to O/C. I'd suggest you try to keep your GPU below 90. Although even thats a little extreme. I wouldnt like to see my GPU go much higher than 80 degrees. Precision X has some nice monitoring software.
As for the actuall overclocking itself. try not to jump to a high one straigh away. Increase you base clock by about 5-10mhz at a time. then play a game for 20 mins or so to make sure it's stable. Also keep an eye on thoes temps. I wouldnt worry about overclocking your VRAM too much for now. It will have little to no effect on performance.