The Biggest promise of NVIDIA's new SLI GPU-teaming capability may be the ability to upgrade on an installment plan. By building an SLI-capable system with a single graphics card now, users give themselves the option of adding a second card later for nearly two times the rendering power. For most of us, the most realistic and affordable means of building such a system is NVIDIA's GeForce 6600 GT GPU. At around $200, the 6600 GT seems ideal for SLI. But does a multi-GPU solution with $200 cards make sense in the age of killer $400 cards and eBay? Tough question. In order to answer it, we've tested a pair of Asus's sweet GeForce 6600 GT cards in SLI, and we've compared them to thirteen different competitors, ranging from a single GeForce 6600 GT to ATI's impressive new Radeon X800 XL. Keep reading to see what we found.