In the end Air does it all, so you might use that. Have you tried two radiators? Or you could try looping water after the radiator back to the resivor.
I run my radiator system in a freezer. The water resivor, and the radiator. I used a 3.5" deep X 1.5' wide tupperware container. The point. . . Because it's shallow and the water has a better chance of transfering heat to the air, because more of the water is exposed to the air than say a deeper resivor. The Fan & Radiator in the freezer or fridge/ do the physics of it all. Depending on the temp's inside the fridge, running your radiator between the pump and the Water block might heat the water rather than cool it. . . Yes even with wind-chill factor. You might try to but the Radiator after the Waterblock in the fridge. You can also stack pelts. You need a lot of juice to run two pelts. Especially since most run best with 24v's to them. Try running 2 pelts. And if all fails, buy an Intel, if you want to run cooler, heh heh, Just kidding!!!
Good Luck
