Place your bets, folks, because this one's gonna get ugly. On your left: a thunderous triad of AMD Radeon HD 6950 cards running in CrossFire. On your right: the terrorizing threat of triple NVIDIA GeForce GTX 570 in SLI. In the middle: a Tom's Hardware tester just trying to stay alive. The winner? Well, as usual in these benchmark articles that sort of depends on what you're doing, but in general it's the AMD solution and its CrossFire barrage that comes out on top in terms of performance, cost, and even ef