Duct tape, cardboard, & black paint are your friends

...black paint optional...

What I meant was, how is air getting into your case? I think I counted 5 exhausts... they are competing for air. this WILL lessen the air that flows through the rad.

skip the duct for now. Just unplug the three case fans and see what happens, and then, just for giggles, try turning them around so that they blow in. I know, generally you don't put the intakes at the top, but just try it & tell what happens to your temps.

One thing I haven't heard mentioned yet is this:

From your diagrams, the block is the highest point in the system, are sure you have bled the air out of the system completely?