Your motherboard is lga1151 1st gen. It only accepts 6 and 7th gen cpus, not 8th or 9th gen which is lga1151 2nd gen.
The best cpu is the i7-7700k, the i7-7700 then the i7-6700k. Yes you can use K cpus on a non Z board just to take advantage of higher boost clocks.
For quite a few games, like CS:GO or LoL, you will not really see much (if any) improvement as you are still running 4 cores or less, exactly the same as your current i5 does. For the rest, that use 5-8 threads there will be a sizable improvement as now the cpu isn't being choked by multiple thread game code. Can be 10-50fps higher ±.
But you'll still be limited by the cpu IPC (instructions per clock) which for 1st gen lga1151 wasn't much of an improvement over the older Haswell series.
Modern AMD IPC in the Ryzen 2nd Gen is equitable to 8th gen Intel, sometimes slightly better with OC. 3rd gen drops in a few months and will be (should be) better still, hopefully topping 9th gen Intel. Recent history has put AMD as better value, more bang for the buck over Intel, even if Intel still had a slight edge in fps. You had to go over the top crazy, i9-9700k/9900k to really make AMD slow by comparison.
So, decisions, decisions. Spend cash on a cpu that's only going to be an advantage in some games, drop cash on a new system that's going to be slower by comparison in a few months, or wait a few months to get a better chance at higher fps for roughly the same money.
Either way, 8Gb of ram at 2133MHz is killing you. Ryzens LOVE fast ram, 2x8Gb 3000 minimum. Intels are running 2666MHz or better. So if upgrading to a Ryzen platform, that 2133MHz ram will put a serious dent in performance, even with 16Gb. If moving to newer Intel, it's still gonna hurt, just not as much.