Dysthymian Rhapsody

Update your CPU microcode. I was having the exact same issues as you due to my MoBo having an old (Pre-Spectre/Meltdown) Microcode integrated into the BIOS. This can be done by either updating your BIOS entirely or by using UEFI BIOS Updater (UBU) to take a preferred BIOS image and integrate the most recent MCU. If you've the time and the inclination I'd recommend going with the more manual approach with UBU as it can update Microcode and other BIOS components to a more recent version than is provided by the manufacturer. Now my whole setup is running far more stably and I've managed to even overclock my RAM to 3466 (the limits of my MoBo) beyond XMP.

The only downside is in price to performance. Most people limit themselves to a given budget and shopping around for components within that budget instead of choosing the components that they want and then getting them. Yes, the i7-6700k is a phenomenal CPU that provides great performance in a wide variety of tasks. However, in a gaming context, the benefits that this provides are pretty minimal (FPS improvements vary wildly across titles). The extra money you could spend between the 6600k and 6700k you could swap up from a GTX 1070 to a GTX 1080. If you've got the budget for it, go ham; otherwise - get a cheaper CPU and try and find a better setup for your needs.

Aligning your GPU selection to your resolution is a useful tool, albeit somewhat reductionist. Ultimately, it comes down to your specific use case. For example, I picked up a GTX 1080 for 1440p because I planned on modding Skyrim (still can't get solid 60FPS everywhere, but I'm not exactly trying to be resource efficient and optimise where possible tbh). Granted, the majority of games aren't resource heavy or inefficient as modded Skyrim so your mileage may vary. Having some overhead with your games is always nice though; maybe you want to try a reshade or re-texture mod that would cause lower GPUs to stumble a bit. Frankly, I agree with Aytex, if you can do so - do so. I don't regret picking up the 1080 one bit, even though it took a while longer to obtain. Otherwise, the GTX 1070 is a phenomenal card with great performance and an even better pricetag.