The last time I ran SLi was with 6600gt's, and I noticed a huge difference in most of the games I played at the time. Heat was an issue (30c ambient= 105c load on top card, 100c on the bottom w/COD2) as well as the limited memory count, and interface still didnt help. After that, I just went for the top shelf GPU's instead of running twin bottom feeders. I havent tried SLi yet on highe end GPU's yet heheh.