I think the fan will be able to cool the water. It is a lot more than what a CPU produces, but perhaps as the surface area is larger it'll be able to spread that heat out over more water so it'll keep it cooler. What I'm saying is, perhaps the surface area on a CPU is some kind of bottleneck but since the surface area on the GPU is much larger it might deal with the heat better.
I don't really know. That's just what's sitting in my mind at the moment