One other thing you have to deal with is the paint on the GPU core. There is a black outline of paint on all the nvidia GPUs afaik and it will hold the heatsink like 0.001" off the middle of the core, which is well bad. Some of the soutions people have had is making a coper slug from a penny, and laping it, or gently sanding the edges of the core with the paint on them down (be careful easy way to kill yer card!)
Also, if you use thermal epoxy all you really need to use it for is some little dabs around the edge, than use plain AS3 on the middle, that way you can use a razor to gently seperate the heatsink from the core if you wish to replace it in the future. I did this with my geforce2 ultra, attaching a stock amd-xp heatsink to it, and it worked out pretty well. One thing is for sure, I was only running .2v over stock and the heatsink never even came close to feeling warm, nither did the back of the card under the GPU, I overclocked the crap outa that baby, got it up to like 400/550.
I have also done the same with the 9500pro that I currently have, works great.