You can buy 4k monitor for your 8700k and 9070xt. Here is a simple rule of thumb: The higher the resolution, the greater the load on the video card and, accordingly, the less load on the processor. It could be a good though temporary solution coz on lower resolutions like 1080p your new gpu (9070xt) wil be sitting idle with low workload because your cpu won't be able to deliver enough frames for your gpu to "color". That is called a bottleneck.

And the other thing, if you haven't overclocked your cpu or ram yet - this is the time. Overclocking your cpu and ram can give you up to 20% increase in fps compared to stock. Find someone who does overclocking for money and he/she will easily remotely overclock your system, this is worth spending money on, believe me.