Well i've RMA'd a lot of cards, and they've all been accepted. The only trouble I had was with my 8800gt that had a faulty fan, but you had to play for hours for it to show up. And when it showed up, it was unreal how noisy the rattle was.
The RMA tester argued with me for over a week
, but finally it started to do exactly as I'd said. You've done enough tests on your own pc...if you can try it out on a friends pc and it does the same thing? That gives extra credibility to your arguement if you need one, and most importantly you know for a fact that something is wrong with that card.