Congrats on the watercooled build, that's quite a beast your creating. Have you considered using a separate liquid cooling system specifically designed for the GPU, it might help mitigate any thermal throttling or other issues with water flow.
That sounds like an insane build man, 10k cuda cores is gonna fly through those renders in no time. Are you using an NVLink bridge to hook up those GPUs or just going with the PCIe route?