The video card block probably has less restriction on the flow of coolant so more coolant is able to pass through that block than the CPU block, therefore better cooling.
As for the video card and res fitting problem, not sure what to do there really. I would say to mount the res horizontal in the top of the case, but that might not be functional.
Might be able to mount the radiator up top and put the res and pump down in the bottom, but not really the right setup for that either, 140mm fans up top and all. Would it be possible to mount the radiator in the front of the case where the three intake fans are? Not sure on the size of the fans or the room available there. there are options, but I am unable to really size things up and get a good view with the pictures.