Where would you spend $$$...new CPU or a GPU water block?

I would say maybe the 58003d, but I would propose something else. I will also explain why.

Save the cash for the new Zen 4 cpu, mobo, and DDR5. (IF you can wait!!)

Why?

My Rig - I have a 5900x(X53 Kraken), 32gb of RAM 3600, Taichi x570, P5 NVME, and a 7900 XTX Merc 310. Disclaimer, I do not use VR yet. I also utilize PBO and undervolting for the cpu. Still testing all methods for best single and multi core OC. My cpu is the bottleneck now, until MSFS takes advantage of all cores.

So why buy Zen 4? The max boost clock, higher Ram speeds, and you would be buying into a platform that will be viable for years, while Zen 3 is maxed out.

If you buy a 58003d you are stuck with the last gen tech. If VR is your goal, and continued VR fidelity, save and buy into the new Zen 4. I also have a rule, never buy a new CPU/GPU of the same gen(Ryzen 5000/i12000 series) unless it is for repair and replace purposes. The gains are not worth the investment, in my opinion.