To be honest with you I think there is very little difference between the two. I had HD cooling on my 04 3/4 ton off-road 4x4 with snow plow prep. and could see no difference in it other than a slighly larger trans cooler as opposed to a truck with standard cooling. The radiatior looked to be no bigger than a standard duty.
I was expecting a huge radiator like in 86 W250 with max cooling. Big difference between it and a standard radiator.