Depends on what you're paying for the 1070. I play regularly at a weekly LAN party and 2 of the several systems have i5s, one has a 1070 and one has a 970. Both perform similarly in older games, as they aren't taxing, but when playing newer games, the 1070 has a clear advantage at 1080p. It gets smaller if you increase the resolution, but with your 144hz monitor and assuming you have G-Sync, a 1070 will be anywhere from 30-50% faster in certain games and look smoother.
The real question is how much you have to pay for it, because of high prices, it might be worth it to wait for a deal to come around or some kind of promotion, as the 970 can still handle modern titles by dropping a setting or two from ultra to high.