yip..why would you want to cool it after the block and mix in the res where most of the water would be warmish then pump it to the block. Seems more efficient to pump the warm water from the res through the rad to cool it just before hitting the cpu.. my theory anyway.
Nope, because you want the water to go right into the rad after it comes through the blocks. The water is imediatley cooled, then that cool water will go right into your res. You don't want warm water in your res. do you? So now you have cool water being fed into your pump and right to the blocks.
Correct answer is it doesn't matter. Water thoughout a closed loops will be very close in temp everywhere. I personaly do pump-rad-cpu-gpu-gpu-t line. But I have been assured that the only absolutely necessary thing is that your res or t-line is right before your pump. The rest is preference...