What will the computer be used for? I HIGHLY doubt you need 8GB. I would go with the 4Gb version of that RAM and put the money saved into a decent PSU and upgrade the GPU to at least a 5770. If you're going to be gaming on this system, what resolution does your monitor run at? That's the #1 deciding factor on what GPU to get.
Thermaltake makes a few decent PSU's, but the one linked above is NOT one of them. The little red voltage switch on the back is a dead giveaway. That means it doesn't have active PFC. The little red voltage switch means turn and run. I wouldn't put that PSU anywhere near one of my computers. It also has very low efficiency (72%). Getting a quality PSU is the key to a stable system. You're best off sticking with known quality manufactures which include Corsair, Seasonic, Antec, PC Power & Cooling, and the newer OCZ models.