Also, CPU and GPU blocks have different flow resistence. One block will end up getting more waterflow than the other. Even if you did get lower GPU temps, that would be at the cost of higher CPU temps.
very true, I have seen the affects first hand, once I re-config'd my loop, from a 'dual loop' back to a single, I noticed lower load temps for the CPU and a lower overall temp delta, due to the increased pressure.
*adding another rad, might lower your delta some, but dont expect idle temps to drop. Your adding cooling at the cost of water pressure...not always a good thing. Although if you have really low restriction blocks..it might be advantageous.