I agree that you will get artifacts (crazy annoying pixels randomly showing up on your screen) before you hurt your video card. Just up it until you get artifacts and then back it off a little. Remember, you have to get your GPU hot (ie run it at full capacity for a period of time) to be able to check for artifacts or check that you are artifact free.
Doom3 is a good test. Run Doom3. Hit CTRL-ALT-~ (tilde; beside the 1) and a console will pull down. Type timedemo demo1. A demo will run. Run that a couple times and check for artifacts (usually begin to see them in the middle of the screen).
|Actually I have found the optimal to be a tad on the conservitive side.
I disabled testing on my GPU, and it allowed me to get to 378/798 Artifact free.
How did you disable testing? (ini edit or is it an option?)