I’m curious to know if it’s worth upgrading my i9 9900k to 12900k because I’m rendering with the GPU or just upgrade the GPU?
It’s not only the CPU but the motherboard and ram and … just to be 20 % faster ??? ( see here https://cpu.userbenchmark.com/Compare/Intel-Core-i9-9900K-vs-Intel-Core-i9-12900K/4028vs4118 or any other comparre site …)
If you are doing a lot of simulations, it might be worth upgrading the CPU, but if you are concerned about rendering time, upgrading the gpu is a much better investment. that 9900k is no slouch, and cpu performance hasn’t really made that many noticeable improvements. over the last 3 generations. GPUs however do show significant performance increases, especially in the RTX line.
Your CPU is very decent for all Single Threaded tasks. No need to upgrade right now. Throw money on a better GPU, more RAM and more nvme’s or SATA ssd’s.