Here's some tips to improve your 3DMark03 score without overclocking:
-Reinstall and update Windows (not very practical)
-Stop all unecessary programs, processes, and services (lists of unnecessary services can be found in the forums of www.extremeoc.com)
-Drop all the DirectX settings...
Subz made a good suggestion. If you're worried about performance, try playing some games with and without your sound card. If there's a perfomance hit without out, then use it. If there isn't a performance hit and you can't tell the difference in quality, then don't use a sound card.
As for...
XMP is unplayable at the high pings that seem to plague all the public servers out there. When I was beta testing it I never got above 60ms, but now I can barely maintain a 150ms ping on most servers. This renders the Ranger's sniper rifle and pistol almost unusable.
I recommend that everyone...
The FPS drops I am talking about are due to CPU usage. The 50% CPU usage you are talking about is actually an average. It's a bit complicated, but I could explain it to you if you like.
It know it would be a real dick move, but I'd love it if the mods reported all of the self-proclaimed bootleggers to Valve. It would also be nice if Valve could actually do anything about it.