Should I upgrade my i7-12700K for an RTX 4080?

I'd keep it unless you're unhappy with performance in a specific game. The 12700K is still a capable gaming CPU, and at 4K the GPU will often be the limiting factor. A new CPU, motherboard and RAM is a lot to spend just because the processor is a few years old.

Check the games you actually play before buying anything. Use a performance overlay to watch GPU utilization and frame rate during a demanding scene, with the frame rate uncapped. If the GPU is consistently near full utilization, a faster CPU probably won't help much there.

If utilization is well below that and performance isn't where you want it, the CPU could be limiting you. Check for frame caps, throttling and other settings too. Low GPU usage alone doesn't prove you need a new processor.

It depends on the frame rate you're chasing. A CPU upgrade is more likely to matter in a CPU-heavy game or when aiming for very high frame rates than when playing a graphically demanding game at 4K. Look for benchmarks of the games you care about, including frame-time or low-frame-rate results, not just averages.

If you do find a CPU limit, a 14700K or 14900K could let you stay on the same platform, assuming your motherboard supports it. Don't expect every game to benefit much from the extra efficiency cores. Higher clocks and cache can help, but the gain varies by game.

Check motherboard compatibility and BIOS requirements first, and make sure your cooling can handle the chip. Also research the reported stability issues affecting some 13th and 14th generation Intel processors before choosing one.