boju :
Lowering graphics too much will shift the work load more toward cpu leaving the gpu working less which you don't want.
Yeah, that's something I didn't point out. Not only does the GPU need to be able to render 240 frames per second, but the CPU also needs to perform its calculations 240 times per second in order to maintain that frame rate. The CPU's calculations might include things like physics, bullet trajectories, enemy AI, network lag compensation, and sound processing. Turning down graphics details might reduce load on the graphics card, but most options won't affect load on the CPU that much. Most modern games simply won't be able to run at 240fps, even if you have the fastest CPU, since the per-core performance of today's CPUs simply isn't fast enough to maintain those frame rates. Game developers typically design their games to maintain at least 60fps on the mid-range hardware that most people are using, but high-end CPUs aren't that much faster, so some games won't be able to get much over 100fps even on high-end hardware.
However, e-sports games usually tend to be less demanding on the CPU, so 200+ fps may be possible in many of them. Something like CS:GO might be able to maintain a solid 240fps. Overwatch might get close as well, but I'm not sure about Fortnite. It needs to handle a lot of players at once, so performance is bound to vary a lot more.
For an example of the limits of low-settings performance, you can look at a CPU review that tests games at 720p to minimize load on the graphics card and exaggerate any performance differences between CPUs. Here's the 720p tests from TechPowerUp's 8700K review, for example, where they benchmark the CPUs using a GTX 1080...
https://www.techpowerup.com/reviews/Intel/Core_i7_8700K/11.html
I believe the settings are all turned up high for those tests, but since 720p is less than half the pixels of 1080p and a GTX 1080 is far overkill for that resolution, the CPU should be what's limiting performance in nearly all of the tested games. It is worth pointing out that these are all single-player game tests though, since reliably repeating benchmark runs in a multiplayer game would be pretty much impossible. An e-sports title like Overwatch would most likely perform better than the average of what's seen here. I'm not sure about something like Fortnite though, since again, a lot of other players are involved. With PUBG, you most likely wouldn't even be able to maintain 100fps much of the time though.