I used ATI Tray Tools driver level overclocking. Overdrive can be hit or miss with these RV570 GPUs. Get the latest release at
in the downloads section. Make sure that you tick the box 'driver level overclocking'
If this is the Sapphire with the reference cooler, you may not be able to get that high on the core clocks due to the VRMs overheating. This was my issue when I had a Sapphire card. I think that they fixed the issue though. I bought my Sapphire in September, then RMAd for the HIS.
All you do is install ATT, then go to hardware, overclocking. Then set the fan to %100, then check the 'driver level' After that, move the slider to OC. We used to have to move the slider on the memory in increments of 27 Mhz, the reference clock, but that is fixed now. Be glad for that sir
Also, Crossfire and single card isn't differentiated in the 3dmark scores. FYI
Also, that 3dmark 05 score is really good. I bet you were running 03.
Here I am with stock CPU, Sapphire single card.