GTX 800 series is on the "tock" for nvidia sans the die shrink. Twins you could always go spend 3k for a TITAN Z
The 700 series was a refresh for the 600 series so the 700 series would be the "tock". AFAIK, Intel is the only company that uses the "tick-tock" cycle as a hard rule though; but, I know what you mean. The 600 series moved into 28nm territory and the 700 expanded on it. Therefore, if we expected the same "tick-tock" expectations from NVIDIA, we should get a die shrink with the 800s.
I would buy a R9 295x2 for less than half the cost of the Titan Z and absolutely crush it. IDK why they advertise the Titan Z as the "ultimate gaming solution" when it doesn't even come close. It is most definitely more of a GPU computing card than anything else.
Or buy my 780Ti's.
If I were upgrading now, I would consider that. I plan on going 4k on the next build though (and Id rather wait until much better 4k monitors are available) so it's going to be awhile. Probably will be doing it once we see the higher end 900s hit the market....maybe even later.