always start with the single most powerful card you can afford, use sli as an upgrade option. As someone coming from sli 660's, and previously from crossfire 6850's i can tell you a single card is always better, less frustrating, works more often. sli is great when it works well, which is most of the time. Quite frankly it only takes one game not to work the way you expect to stuff your experience up. for me i have decided to stick to single cards from now on.