^SLI, that's the whole idea behind it. As much as i hate the moniker (yeah, i do hate this moniker, well atleast an NV's implementation/PR of it lol) when it comes down to this technology, you get can o' whoop ass performance with pair of these; definitelly way more bang for a buck compared to either GTX 680 or 690. Hardly justifies buying one GTX 690; unjustified when buying pair - unless you want excessive performance in latest & future titles &/or got a f***load of cash; or both. Check out the GTX 670 SLI review here - you'll see what you get with pair of these.
P.S. Will actually make me buy Dell UltraSharp 30" LCD for these - PC store near me got this monitor after a years i've being waiting for it to arrive to Israel.