TA4K

I've seen a nice Black and white build on MDPC I think. I saw the thread somewhere on OCN too.

I know Linus would say 24hrs prime blend, using almost all RAM, and for GPU's 24hrs of furmark. I would think that's a pretty good measure of stability.

Seeder. Fixes some pretty big random pool bugs by refreshing it every minute. Nice performance boost, and although it's a paid app on the market, you can get the .apk from the dev on XDA. Does need root though.