I personally used 1mm pads, maybe 2 mm or 1.5mm would work too, but i wouldn't go thinner than 1mm. I used 5w/mk, where did you find the 7w/mk ?
I am curious how much a pad would have to have in order to be used on top of the cpu/gpu
Update for my own project : it seems as if my temps finally dropped severely

I put TP on the chips (rice grain size on gpu, slim line on cpu) and i used the heatsink to spread it. At first i didn't notice any improvement, but now, after nearly 24 hours, its much better. Although i did use Arctic MX-4, there seems to be some minimal curing time...or maybe the TP just needed gravity to do its work and let it spread properly
As for temps reaching 100°C for a short period of time while using furmark in bootcamp, it seems as if this is unavoidable, no matter what. At least temps like this won't show up in games