WHAT? You may say but long ago Tomshardware and others swapped motherboards and tested the results and the results were so close that HAL 9000 said it well:
HAL: Well, I don’t think there is any question about it. It can only be attributable to human error. This sort of thing has cropped up before, and it has always been due to human error.
That aside, you want a board with extra space to let the GPUs breathe. Example at:
Since that's the best CPU that may be the best for your application and gets you ready for the RTX 2080's or what's next.
I would like to build a PC with two GTX 1070 for gaming and mining. What is the best Motherboard/CPU that can use the most of the two GPUs? In terms of price and performance.