I think the top score is within reach for ya. I was able to get 41k myself with my dothan at 3.1GHz...so you should have plenty left.
Tweaks...well...I've got as many as you'd need, but how much would you be up to?
Biggest and easiest one is to set LOD. In ATiTool under Settings, go to "Driver Tweaks" and set Level of Detail to +3.0, and make sure that Catalyst AI level is High. In ATi's control panel or CCC make sure everything is turned all the way down as far as quality settings go.
Then, use a customized test order when running. You can choose which tests to run in this window. Select tests one at a time.
Start with dragothic low, then lobby low, car high, drag high, lobby high, nature and then car low. Car low is the only test that you want to run more than once. It usually takes about 5-10 runs to get a good one that sticks out. It'll usually be about 300-500 points worth above an average run.
Also, you'll probably find it beneficial to tighten your X800's memory timings to the ones shown
here. Expect to lower your memory clock to around 600 flat though.
The more time-consuming ones are loading up windows 2000 and using Cat 4.12 instead of the newer ones.