High refresh gaming is one area where Ryzen does not excel at and you are more likely to see a CPU bottleneck, though how bad it's going to be will vary depending on the game. Part of the problem with 240Hz is that even the i7 7700k can be a bottleneck in some titles and hitting 240FPS simply isn't possible even with the best GPU available. It really comes down to the games you're playing. If you're playing lots of big open world titles, you're more likely to be CPU bound, if you're mostly playing shooters with small to medium maps and player counts or racing games you're more likely to be GPU bound and would benefit from a 1080 or even 1080Ti. Frankly I don't think moving from a 1070 to a 1080 is a big enough of a jump to be worthwhile unless you're planning on selling your 1070 for an inflated price to a miner. The 1080Ti is a more appreciable jump, but you might not see that at 1080p resolution due to CPU limitations.