7900 any day. SLI isnt going to every be 2times as fast. It is good but not that good. The 7900 blazes FPS rates everytime. And the option to get another in the future as you say is there with SLI. I think also that the comparison is that the 7900 will not be as good as a pair of 7300s but then it is more of the fact do you really want to struggle selling the old ones on if you want to upgrade in the future as then you will need to get 2 more to upgrade.