Try reversing the flow. The way I see it, the water will pass through the radiator (slightly warm from the CPU), then it'll travel to the GPU blocks and pick up even more heat, then it'll pass through the pump which will heat it a bit more, and then you'll have really warm water passing to the CPU again. I think the opposite flow direction would be better. But thats IMO.
List of updates to do by summer: (1) New PSU: Seasonic S12 600W, (2) New OCZ Phase change or WC, (3) Sleeve cables: white, (4) 1 More 12" CCFL, (5) Some dremel action: circular side window