Your i7-860 is not limited to a single video card. You could do SLI with a GTX 470.
It is capable of handling as many as you can install on your motherboard, providing you have enough power.
You forgot to mention what motherboard and power supply you're working with.
I have a Intel DP55KG Extreme Series Desktop Motherboard which supports SLI but only has one 16x port, the SLI would be dual 8x then :S, is that a problem? is there a major difference with dual 16x?
I have a Corsair certified 850TX series