Nvidia revealed key details [tomshardware.com] about its upcoming "Pascal" consumer GPUs at a May 6th event [anandtech.com]. These GPUs are built using a 16nm FinFET process from TSMC [wikipedia.org] rather than the 28nm processes that were used for several previous generations of both Nvidia and AMD GPUs.
The GeForce GTX 1080 will outperform the GTX 980, GTX 980 Ti, and Titan X cards. Nvidia claims that GTX 1080 can reach 9 teraflops of single precision performance, while the GTX 1070 will reach 6.5 teraflops. A single GTX 1080 will be faster than two GTX 980s in SLI [wikipedia.org].
Both the GTX 1080 and 1070 will feature 8 GB of VRAM. Unfortunately, neither card contains High Bandwidth Memory 2.0 like the Tesla P100 does [soylentnews.org]. Instead, the GTX 1080 has GDDR5X [soylentnews.org] memory while the 1070 is sticking with GDDR5.
The GTX 1080 starts at $599 and is available on May 27th. The GTX 1070 starts at $379 on June 10th. Your move, AMD.