Hmmmm....Your question comes up from time to time and it gets kind of crazy. Last time I looked there were 42 different brands of thermal compounds, liquids, paste, and pads for cpu heatsinks. The performance comparison charts provided by manufacturers always indicate their own product is the best. Results in independent tests always vary. Sometimes the results are close and sometimes they aren't. On top of that a lot of the veterans here have their own favorite thermal compound they swear by.
It is safe to say there is no clear cut, across the board, hand down, best thermal compound. I would suggest you try a few and see what works best for you.
As for your build, if you only have one ATI Radeon 5870 video card, then a 1,000 watt power supply is total overkill even for extreme overclocking. If you are planning on using multiple video cards, then it would be different.
Yes I know that the 1000W is overkill, but I plan on putting more GPUs in the future so I thought why buy a small PSU that I am going to have to upgrade later when I can get one now that will power my system for a long tome to come (plus it was on sell XD)
I think I will try the PK-1 for now, but I already have some Silver being shipped so I will try it when it come in