2nd generation Sandy-Bridge saw the first 'K' overclocking cpus, which split the cpus into locked multiplier or unlocked. OC was thereby shunted to BCLK, which was a disaster waiting to happen. Only certain cpus with unlocked multipliers like the pentium G3528 deviated from that.
Z mobo won't change that, a locked cpu is a locked cpu, it just has an unrestricted bios that aligns with a K cpu's unlocked multiplier to grant OC. Granted, there are exceptions, but as a general rule in order to exceed the stock default settings requires a K&Z.
Generally, resolution has little to do with the cpu, very little if any difference to the cpu between 3440x1440 and 1920x1080, an object is still an object. Frequency is different. The cpu needs to tell the gpu to put that object at a certain location 100x a second, vrs standard 60x a second, so yes, the 100Hz monitor can require a certain amount of cpu horsepower. Resolution is just about all on the gpu, and at 3440x1440 you are pushing the limits of what a 1060 can do, and still get decent fps at decent detail settings. You'll get ultra in very few games, especially at 100Hz or better.
Where you are at is right in the middle,damned if you do, damned if you don't. There's many games that handle an i5 no worries, but require gpu horsepower to get good fps, so for those games, the i5/1070 will be the best option. However, there's just as many games that not only benefit from the i7, but need the increased ability the i7 brings over the i5, cpu intensive games, that have a lesser reliance on the gpu. Then the i7/1060 would be better.
Honestly, for the price, I'd go with Ryzen R5 1600 and a 1070. This'll get the HP needed for both cpu and gpu without the limitations of either the i5 or the gtx1060.