Who says you have a gpu bottleneck? Some stupid online calculator with a link to a website that'll sell you a 9100F to fix it?
That's an extreme case of BS. None of them are even close to accurate. Or realistic. When it comes to cpus and gpus there's no such thing as a bottleneck, because a bottleneck is something that slows down the flow of info. Neither does. They both work at 100% ability, all the time. In some games like modded skyrim, they are extremely hard on the cpu, so you get low fps output and the gpu isn't even breathing heavy. In some games like CSGO, the cpu can put out far more fps than the monitor can use, and even then the gpu is half asleep. In some games like BF5, they are so graphically demanding the cpu is under used because the gpu is slammed to the wall. In neither case is the flow slowed down, it is what it is.
The 6/7th Gen Intel are lga1151 v1. The 8/9th Gen Intel are lga1151 v2. Same pin count, different socket.
Yes, experts have successfully modded an 8th gen cpu to get windows stable (ish) on a 7th gen board, but could not get anything else to actually work. As soon as a load was applied, it crashed. For all intents and purposes lga1151 v1 and lga1151 v2 are totally incompatible sockets.