Are my cards running at full speed?

I have 2 6600GTs in SLI, and am very happy with the performance, but obviously I want to confirm everything is working properly. I know both cards are running - there is an option in the drivers to show a bar graph of the load balancing whenever 3D apps run.
But something funny happens in 3DMark03. If I reinstall the drivers then run 3dmark, I get 14,250, and it lists the core/memory speeds as 500/1000. But if I run it again later I only get 10,000 and it says the core speed is only 300.
Are the cards sticking at 2D speed (300) instead of switching up to 3D speed (500) ?
Obviously I don't care about the 3DMark itself, but it does suggest something's wrong. Any ideas?

EDIT> OK, I've downloaded 3DMark05 and gone up from 71.84 to 71.90 drivers.
3DMark05 reported 4440 (@300MHz) using 71.84, and 6210 (@500MHz) using 71.90, and seems consistent.
3DMark03 seems to be scoring in the 14,000's consistently now, but still claims 300MHz!
The important thing is it isn't slowing down any more, so that'll do me! :)