Currently I'm running at 875MHz core clock and standard memory clock. Voltage is stock, I haven't played with it yet. I got it up to 925MHz with stock voltages, but then it became a bit unstable at some scenes in Crysis. It was stable again at 900MHz, but I just dropped it to 875MHz for the more quiet fan operation I get then. I want to start playing with the voltages a bit, I'm quite sure I'll be able to hit 1000MHz on the card, the Cyclone cooler keeps it cool as a cucumber (at 900MHz stock voltage & 100% load for 10 minutes the temps never exceed 60'C).
Gigabyte 256bit (early production) with asic quality of 68% and stock bios I got 930mhz on 1.087v. I don't run Furmark but instead pefer to run games and compute apps. topped 73c while running bitcoin.