I'm using air cooling. Gigabyte X570 Pro, RTX 3090 FE, be quiet! Pure Base 500DX mesh case with four 140mm fans currently. It's not quiet under heavy load!

The GPUs have gotten improved thermal pads. The 8 core Ryzen 3700X is a 65W model. It appears to be fast enough not to be a bottleneck for this purpose. 1200W PSU.

I may swap the fan in front of the GPUs for a high-rpm model.

Also for longer runs i throttle the GPU power draw. It doesn't cost much performance.