Maximum PC: If you poke around Nvidia's website, you may notice a new addition to its GeForce graphics card section for desktops. It's the GeForce GTX 760 Ti, a new part that's intended for OEM partners. Product images and full system specs are posted on Nvidia's website, and at a glance, this appears to be a rebranded GeForce GTX 670 graphics card. Let's have a look at what makes this thing tick.
Nvidia Maxwell comes out in March so anybody wanting a real upgrade should wait till then. You could get away with anything from GTX 680 equivalent to a GTX 780 for under 300$!
"My guess is"
GTX 860 = GTX 680 - $200
GTX 860ti = GTX 780 - $300 - $350
GTX 870 and GTX 880 would be 40% - 50% increase over Titan! Price could be anywhere from $500 to $750 accordingly?
Assuming it's GK110 and all SMX unlocked it's totally possible that you can see that type of performance gains from next generation reference cards since it's a die shrink plus a new architecture!
For comparison see GTX 580 against GTX 780/Titan. The real GK110!