Xion, this is the first time I have chimed in but have been watching from the start. The build looks great and I can't wait to see it completed! As for the rads, they should be fine. I'm running the same rad on my CPU loop with an i7 920 and Heatkiller 3.0 LT Block and at 4.2Ghz I have not hit over 60C while folding, so you will have no problem!

As for the 5870's you will love them! I just sold my 2 4870x2's and am running the XFX 5870 and I'm loving it. I will go Crossfire too when I get back from deployment. If you plan on watercooling, may I suggest the EK FC5870 Plexi+Nickel waterblock:
http://www.ekwaterblocks.com/shop/bl...70-nickel.html
Not only does it look great but it performs like a beast! I have my GPU at 900/1300 OC'd and I have not hit over 33C while running Furmark and I idle on Windows 7 at 27C!! I'll try to get you some pics of mine installed with some temps if your interested.