First of all, 790i is an Nvida chipset for LGA 775 socket cpus only (Intel Core 2 Duo, Quad, Extreme, etc.). The 790FX is an AMD chipset for AMD AM2+ socket cpus (AMD Phenom). The 790i is DDR3 so you can get faster memory for a much, much higher price. It also supports nvidia's SLI cards as well as wolfdale and yorkfield support. The 790FX supports AMD's Crossfire X in which you can run up to 4 GPUs in scaling mode (sorta like SLI, but more cards). The nvidia chipset is running intel, so right now it is faster than the AMD cpus. You can also now run 4 gpus in SLI using 2 9800GX2 cards. If you are an enthusiast with money to burn, get the 790i since it has DDR3 and you can add in an expensive and nice Intel QX9770, or whatever is the fastest yorkfield now. If you don't need DDR3, but still like the intel/nvidia option, get the 780i. It support everything the 790i does except for DDR3.