Aaaahhh.....elegance. It seems that it is always the goal. A noble one at that!
I think that I can see what you're getting at a little better. So a rad is working more efficiently if it's absorbing/dissipating more heat relative to the temperature of the system. I wonder if an "open core" radiator would be more efficient that the tubed ones that most of us use. Something like this (it's not the most idicative drawing, but I think you get the point):
