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

FYI, I just realized I have the same case, but the QL RGB version:

https://www.corsair.com/us/en/Categories/Products/Cases/Mid-Tower-ATX-Cases/iCUE-5000X-RGB-QL-Edition-Mid-Tower-ATX-Case/p/CC-9011233-WW

If I’m reading your post correctly, you kept the side baffle on to direct air over the motherboard. I took mine off and added 3 side intake fans - I did not think the side baffle was useful if you want to add those 3 side fans. In total, I have 3 front intakes, 3 side intakes, 3 top exhaust (ML fans on radiator), and 1 rear exhaust. Even at lower RPM, this is sufficient to cool an overclocked 13900K and overclocked 4090 that can pull 550W+ under load. The 4090 can generate some impressive heat when power consumption climbs over 550W.

(Excuse the puke rainbow RGB… this was taken shortly after building)