If the current system is meeting your needs, no need to change.
No matter how cheap or what 'promo' you're getting.
^I have to agree.
OP, 90 FPS at 4K is pretty good results. Some of the new games use ridiculous amounts of VRAM, RAM, and CPU, but they can be troublesome even on the newest hardware.
The new Intel CPUs that have both P and E cores are a pretty decent jump from what you have, but you wouldn't make use of it much unless you bumped up to one of the new beast GPUs, which IMO are overpriced and oversized.
Between the economy the way it is right now, the high price of PC components (especially processor based ones), and the horrible condition PC games are releasing in, it's really not a good time for a new PC build or even a major upgrade.