Hope I'm not too late to this party.
https://www.youtube.com/watch?v=K9EJNa0y524 (Benchmarks start at 2:42)
This should help you out on your dilemma. It's not necessarily a 1070, but he does bring up good points. I'll let you watch the video but TL;DR It's up to you to decide whether a couple of frames is worth upgrading the rest of your system (assuming that you're gaming at high resolution).
Don't worry I'm in the exact same boat as you are.