I was kinda hoping to not post this, as one site creates a story based on half facts and then 2 news-posts later on other websites, it all of the sudden becomes a fact. Okay, let me write it the way it is. There is a rumor that there will be no new graphics card releases from Nvidia in the mainstream to high-end segment until later this year. Rumored is that in Q4 Nvidia will release the GeForce GTX 880 and GTX 870. Both cards would still be based on 28nm due to 20nm complications and both cards would be based on a variant of the GM204 Maxwell GPU. 

Nvidia Maxwell's GM204 GPU could have 3200 Shader processors and almost 7.9 Billion transistors. The DirectX 12 compatible GPU would be SSM enabled, streaming multiprocessor Maxwell. The product would get 200 TMUs and 32 ROPs offering a 5.7 TFLOP/s single-precision floating-point throughput. Memory you are looking at a 256-bit wide GDDR5 memory interface with 4 GB being the standard memory amount.

With a memory clock-speed of 7.4 Ghz that would get the product a 238 GB/s memory bandwidth. The reference products would get a 900 MHz core with 950 MHz GPU Boost and a 230W board power. 

The specs are to be considered highly speculative.