My estimation would be that a 1070 would be more than plenty of horsepower to push 1080 all day long at an easy 60hz. The 1070 is easily comparable to some beefy 980s.
A multipurpose 60 hz monitor with a decent price ( just over $100) is the Asus V239H-P
http://www.newegg.com/Product/Product.aspx?Item=N82E16824236288
A decent 144 hz monitor for a good price ( a little over $200 ) is the AOC G2460PQU
http://www.newegg.com/Product/ProductList.aspx?Submit=ENE&DEPA=0&Order=BESTMATCH&Description=AOC+G2460PQU+&N=-1&isNodeId=1
Ask yourself this, " Do I need 144 hz? "
For less than $300, you can get a decent 144 hz monitor that will take advantage of even your 970 if you tweak some settings. I have found that monitors with high refresh rates are best utilized in FPS and faster paced games where reaction time, position, and timing are all key. If you are more of a casual gamer 60 hz might be enough for now. If you are a competitive FPS player who cant live without playing CSGO- maybe the 144 hz monitor is the way to go. Other games not so much- and 60 hz is more than enough.
In terms of GPUs - the 1070 is the best buy pound for pound in terms of price/performance. The new Pascal architecture has made this a beastly card at a reasonable price. The performance would be more than enough for 1080p gaming and decent for 1440p gaming.
Its a tough decision. You are truly right at a threshold where you must weigh options.
OPTION 1:
Buy 144 hz monitor- save some money toward an upgrade in the future and enjoy the benefits of a high refresh rate (believe me- you can tell a difference provided your card can push that many frames). I think a 970 is still a decent card. Cost - about $200-$300
OPTION 2:
Buy a 1070 and enjoy buttery smooth frames maxed at 60hz/60 fps in most titles - cost : $400-$450
I would go with OPTION 2 personally . The monitor is always something you can push back a little further. Once you have the 1070, I think the 144 hz monitor is a natural progression when you get a little more money together.