DDR3 is a complete waste of money. nVidia's Intel chipsets are not very good at all either. The 790i has been borderline terrible with data loss problems with overclocked among other issues.
Get this instead:
4GB DDR2-800 4-4-4-12 RAM
X38/X48 chipset motherboard like Asus P5E
If you are mainly gaming pick up an E8400 over a quad core, otherwise Q9300 or Q6600 for max overclock.
1200 case, 900 is tight.