Nvidia has only been optimizing game drivers for their Maxwell cards(9xx series) and left their Kepler cards(7xx series) out to dry. In games such as Witcher 3 Nvidia owners are seeing budget GTX 960s perform better than GTX 780s for no reason other than driver optimizations. It isn't a matter of new tech vs old, it's just Nvidia's attempt to force people to purchase new cards. Terrible practice considering many of their angry customers purchased these cards less than a year ago for very large premiums.
I've done my research and not everyone with kepler cards are actually complaining. but Nvidia should update drivers for these cards to play the latest games.
It's a real shame because the 780/780Ti and Titan Z were beasts. This is not something I've read or could support with facts, but I have a hunch they've given up on them because of how ineffective they'll be compared to AMD's units that are able to take advantage of asynchronous shading upon the implementation of DX12. Just a thought.
Titan Z still is if you are considering 2 gpu's in one and the 780/ti were really good cards themselves! Everyone should have the boost that DX 12 gives though. I mean from all I've read on the interweb, even the little mobile processors will be able to benefit.
Unfortunately for Nvidia owners with Kepler(700 series) and earlier cards(all the Titans save for X too btw), they were built without one of the key requirements to benefit from DX12 - the previously mentioned asynchronous shaders. DX12 actually enables a greater load to be placed on the GPU relative to the CPU so performance of pre-Maxwell nvidia cards will almost certainly suffer serious performance degradation compared to their AMD counterparts. Hence my hunch that nvidia is slowly pulling support for cards seemingly prematurely in order to get more of the kepler and older owners into the Maxwell series.
Here is a good article explaining asynchronous shading and ACEs - http://www.extremetech.com/gaming/202407-directx-12-liquidvr-may-breathe-fresh-life-into-amd-gpus-thanks-to-asynchronous-compute
The 7870k has 8 Asynchronous Compute Engines.
How are the 700 series not built without one of the key requirements to benefit from the new API? http://www.dsogaming.com/news/report-directx-12-to-be-exclusive-to-windows-10-nvidia-lists-dx12-compatible-gpus/ Nvidia says' that even the older generations like Fermi.