You definitely need a 144hz monitor for a GTX 1070 - anything past 60fps on a regular 60hz monitor is almost pointless.
Barebone 144hz $268.99:
https://www.amazon.com/BenQ-XL2411Z-...qid=1470845378
Gsync $399.99:
https://www.amazon.com/Acer-Predator...qid=1470845670
If you are interested in Gsync, you must use a monitor that specifically states that it supports it - not freesync or just adaptive sync. Gsync is a nice feature, but not 100% necessary - if your budget is $250, then I wouldn't worry about it.
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This is so wrong, do not listen to this. While a higher refresh rate isn't as advantageous in a MMO as say, a FPS, it's still a night and day difference in fluidity. I don't know what kind of pc the guy who posted this has, but I have a 4930k @ 4ghz and only a gtx 970, and my FPS rarely goes down to even 60 at high settings. The only time it does is in extreme situations such as the new legion invasions. During normal PvP/raiding/questing/etc, I'm always hovering around 85-120+ and the higher refresh rate is EXTREMELY noticeable. As long as you're maintaining above 60fps, you're going to see a difference. If you have a gtx 1070, your FPS will be very high in WoW and you'll take full advantage of a 144hz monitor.