If you go Sli, im seriously considering to spit in your mouth.
lol it is the worst investment ever. If you were to go SLI, you might as well sell your 8800GT and buy a 3870 X2 for the same price. (bad example since its an xfire card.) but you get what im trying to say.
For the price you would go to SLI, you can buy the best GFX card and it would smash the two cards in sli.