Those GPU's aren't even on the market yet. And when they hit you can expect them to be in high 800 dollar range. The Titan GPU's start at 980 and go to over 3000 dollars.
Currently the NVidia line stops at the 780 then jumps to the Titan line.
You going to shell out that kind of money to just play video games? If yes, that's insane. You're looking at around 3000 dollars when you're done.
And if that's your plan 870watts ain't gonna get it. You need to look at a 1000watt power supply**. Be sure to get a UPS cause a power surge or a lightening strike is going to fry your multi 1000 dollar rig. I have a 125,000 dollar guarantee on mine. If a blip gets past it, APC owes me a ton of money to replace it.
** 1000watts Platinum for under 300 bucks: http://store.antec.com/highcurrentpr...platinum.html#