One more thing to consider, running 2, 3 or 4 vid cards means you need a massive psu not to mention the heat they are going to emit so stock cooling won't be sufficient anymore either. There's a bit more involved than just cramming a bunch of vid. cards in your computer case. A system that hardcore needs to be designed from the ground up for that purpose with sufficienct power and cooling in mind. It will take a lot of fans to keep that system cool, so if noise is a concern you may want to look into liquid cooling.