The fastest gaming CPU is the i9900k, currently $529 on newegg vs a R7 3700x currently $298 on newegg (same number of cores and threads). If you consider any cpu under the 9900k from intel you might as well go with Ryzen, the i5 and i7 can't compare. Your MOBO options are also going to be cheeper for Ryzen. Just pair it with a good B450 and you are golden, or spend a little extra for x570 and you will have gen4 PCIe, Ryzen 3000 is automatically supported, and there are other features that will future proof your build. You will also be able to upgrade to a newer or more powerful Ryzen CPU down the line since AM4 will continue to support new chips, I belive till 2021, but don't quote me.
In the end if you are only going to use your system for gaming, your GPU is the most important component. Save money on your CPU and MOBO, and put that money towards your GPU. Think about it. average $200 Z390 board, $529 CPU, thats $729 for your mobo+cpu combo V.S. $114 b450 tomowhawk max and $298 Ryzen (that comes with a cpu cooler so no extra money needed). thats $317 you can put towards your GPU. So if you were already planning to add a 2070 Super, that extra $317 can get you a 2080 TI.
You also need to take your monitor into account. A good 1440p monitor can make a world of difference.
edit: but to answer your question, the difference in FPS is negligible, you probably wouldn't notice a difference.