Grunt, my card is the newer kind. I can tell cause yours takes two slots, mine only takes one. But I do have plenty of cooling- I've seen to it. The ambient temp in my computer never exceeds 75*F by more than a few degrees, even after hours upon hours of rigorous gaming. I've also got my A64 2800 (s754) oc'd from 1.8 to 2.16 as well, but it just PEAKS at 50*C only after four plus hours of rigorous gaming.
So I'm sure that eliminates cooling. I have 1x120mm fan for intake, 1x80mm fan on the side panel as exhaust, 2x80mm fans as exhaust in the rear of the case, the psu has a 140mm fan for exhaust, and I have a Cyclone blower under the vcard to exhuast most of the hot air produced by my card. So I do doubt that cooling is a problem. Also because my card has NEVER exceeded 55*C even when it was at 515clock/ 1GHzmem.
Do you notice any abnormal pictures or such with your card at those speeds? Cause as soon as I set my card to 530Mhz core colors would be missing, and entire textures would be missing, as soon as I started a 3D app. Even in screensavers the picture would be all "out of wack". So I figured that maybe the memory was too high, and dropped it to stock speeds while leaving the core clock at 530. Same problem. I tried the reverse, putting the memory back up there (I belive 1.1GHz) and the core at stock speeds. Same problem.
What score do you get in 3DMark05 at those speeds? I'm sure that card is rather fast cranked up there like that. Wish mine were.