In your scenario it is unlikely to be worth the spend. However if you find you have bad 1% lows / stuttering and its bothering you, then you should consider the X3D. Having access to the memory quickly severely helps smooth out gameplay because of the increase in lows. Being on a good low latency DDR4 you should be fine just letting you know what you would gain if you run into that.
A good practice when comparing CPU's is to look at their FPS benchmark in 1080, then look at your gpu benchmark in 4k. If the gpu benchmark in 4k is lower than weaker CPU you are considering, you won't gain anything by spending more. This gets more complicated when comparing specific games and cpus with a different numbers of cores, etc. But should give you enough to get started.