Well you are still limited by air a little bit. You'll need a big enough radiator or a chiller system in order to remove the heat from the water. Observe&report did a water cooled cab using CPU components. Worked decently well.
I've always wanted to drill holes through the heatsink base so that water could be ran through the heatsink itself. Just to aid cooling, plus have backup cooling of the heatsinks themselves in case the water pump failed.
Hmm, I wonder if .25" diameter passages would be enough to remove heat.