i7 is better overall since it is hyper threaded and can help with multitasking like streaming while playing games without a significant loss in FPS.
Higher refresh rates are more or less going to be bound by your GPU and it's ability to maintain that level of FPS in your games.
If you have a GPU that can perform at this level and you have the budget for the i7 then go for it.
Assuming you already have a Z370 board perhaps it is in your budget or you have the option to wait just a little bit to get the budget and go for a K series. If so, then go K series for overclocking and getting even more performance out of your CPU.
If you don't have the Z370 board yet and are planning to purchase then I recommend you consider going with Ryzen instead. Unlike Intel, ALL Ryzen chips can be overclocked. The price for a cheap B350 chipset board is about the same as a Z370. (B350 or X370 for OC on Ryzen) and unlike Intel, the AM4 platform will support the new Zen2 CPU's from AMD whereas an upgrade with Intel will require purchasing another motherboard just to get the new CPU.
But out of those two options I'd say go with the i7 if it's in your budget.