Take it with a grain of salt but TPU came across some leaked 3DMark scores of what is claimed to be the GeForce GTX 870. If these results are genuine, the card delivers about roughly the same performance as a GeForce GTX 780, which would be pretty good considering the price of this new model should be a lot lower.
The card's CUDA core count is 1,664. Given how streaming multiprocessors in "Maxwell" GPUs launched so far feature 128 cores, this particular chip features 13. Other features read out are 138 TMUs, 32 ROPs, and a 256-bit wide memory interface, holding 4 GB of GDDR5 memory. The sample features clock speeds of 1051 MHz core, 1178 MHz GPU Boost, and 1753 MHz (7012 MHz GDDR5 effective) memory, yielding 224 GB/s of memory bandwidth. The test-bed including a Core i7-4820K "Ivy Bridge-E" quad-core processor.
The card was put through 3DMark 11, in its performance (P) and extreme (X) presets. It scored P11919 points in the performance preset, and X4625 in the extreme preset; which makes the card roughly as fast as a GeForce GTX 780. And these are pre-release drivers, and probably a pre-launch qualification sample altogether. Color us intrigued.