Hmm. I think I got about 425/450 to run on 3dmark 05. Wasn't as good as 420/427.5 tho. The highest overclock is usually not ur best, but I have the highest clock so
What drivers are you using? I noticed that with the stock and low 7xxx My overclock seems to shrink quite a bit..almost nothing to shake a stick at. 77.50 works wonders for me =)
EDIT: You know, this is similar to what happened to me one day. I had one of the higher 77 drivers installedand for the longest time I could not push my card past 428 and 857. That was IT! Then all of the sudden one day the card started to get cold, like 5-7 degrees colder then normal. I was @ 46 idle no aftermarket cooling or AS5. Then I could really push this baby high. and now the temps have went back to what they normally were, probably cuz I recently unlocked stuff and it's summer now.