Water is a great conductor of heat, but it also has great capacity. The temperature difference between inlet and outlet on a radiator is very minor. The water still has the capacity to absorb more and more heat up to the boiling point (or more in a pressurized system). At the heat loads and temperatures of PCs, this is just not that important.
I have described what is typical, really any configuration should work out well enough. Never had any issues with GPU temps (not counting now, but I already have a replacement waterblock on the way, with hopefully better mounting pressure) having my CPU pumping into the GPU. I did once put a radiator between the CPU and GPUs, but I really just needed someplace to put it, and tubes I was using at the time didn't lend themselves to another config.
Huh, I need to talk to PrimoChill about the royalty checks they forgot to send me (Effectively the latin word for Remove, so I imagine it was that). Going to have to pick one of those up just to have it, though it doesn't have any Eximo branding.