It will be up to you what you decide eventually to go with.
RAM is not an issue - you can add/upgrade at any moment. it's not complicated technically and pretty cheap. so 8 or 16 does not matter. 8 is enough, 16 is comfortable.
CPU + MB. you can have 25-30% boost from overclocked 6600K over 6500. CPUs are long terms investment these days. with K i5 you can have it for 5 or more years without suffering from perfromance issues. only when it comes to 144Hz monitors, some CPU intensive titles will benefit from i7.
GPU - is the most frequently upgraded part in most systems. the lifespan of mid range GPU is 2-3 years before you need to lower settings to some crap.
470 4GB is withing few FPS from 1060/480.
so if i were on a budget, and would need to make a rational choice, I'd invest in best CPU and MB i could afford and get the good enough GPU for a couple of years.
in your case it translates to i5-6600K + RX 470 4GB. that will do 1080p gaming for couple of years at least. and then, you will only need to upgrade the GPU.
the games you mentioned (witcher 3) are CPU intensive (as most open world games) - so you do need a powerful CPU for that.
what you think is best for you is up to you of course