Presumably, the Vega rumored to come this Fall (October 2016 but may delay to 2017 depending on rumor) will compete with 1080 or even the follow-on to 1080. Nonetheless, I believe Nvidia will do whatever it has to do to provide a faster card -- even if they can only make a few and sell at a loss (as highest FPS in their best card is what defines the brand). So, I expect Vega to perform measurably slower (but not visibly slower) than what Nvidia answers with. But, I imagine the AMD Vega will have other advantages -- like lower cost and better performance in some situations.

In 2018 (??) AMD has an all new design approach coming out called Navi (mentioned by SkateZilla). It's a way to put multiple chips together on one card -- and they act as one chip (not like Crossfire). That approach should be capable of humongous speeds in a very cost effective card (smaller individual chips are much cheaper to make) -- with single card performance advantages. We'll see.

Based on the rumors, I'm leaning towards Vega for myself (this Fall) and RX 480 (in July) for my wife (she does not need the power -- but she could use a new card -- and it will be fun to test). Then, when Navi arrives, I'd probably buy one and "retire" the Vega. Meantime, my two HD7970 still play my games visibly smoothly on "ultra" graphics settings (0 AA).