In cpu bound games the i3 will begin showing fps drops like it does currently. The 1070 would be somewhat overkill for 1080p, would likely stretch its legs well at 1440p. Regardless of the cpu you may not get the max out of a 1070 at 1080p resolution. Similar to running a 980ti for 1080p. The hyperthreading helps an i3 over say a pentium, something strictly dual core but min fps are lower than a true quad core like an i5 or i7. 79-85fps may be fine for a 60hz monitor, a 144hz monitor may be a different story.
It all depends on the system as a whole rather than one size fits all. There's a reason the i3 is touted for being a good budget gaming cpu and not the best gaming cpu for the money. It's not priced to be and it's not, it is what it is, a hyper threaded pentium basically.