A New Computer....(maybe)?

Andrew Price ditched a single NVidia GTX 560 card for two GTX 680's and noticed a decrease--others have reported gains of about 20% on average going from a 5xx to 6xx series GTX. The 760 will be a rebranded 670, after that you are looking at at least $400 per card for any gains*. If you can get your hands on a 560, 570, or 580 card used that might be a good option. I'll be doing some classified-looking myself for a 560. ATI does not support Cycles at the moment, only NVidia.

Andew Price Wrote:

Bought a New PC:
2 x GTX 680 = 36secs
1 card only = 1 min 1 sec

My old PC:
GTX 560 = 46 secs

Not much difference for a $1000 investment
I guess when people said the architecture in the 6 series cards are worse for Cycles, they really weren't kidding.

As far as the chip-set: Intel i7 is my recommendation.

*OEM 7xx cards are supposedly one their way next week (we'll see), with boxed versions available shortly afterward.