I agree, but think it's a combination of both. (Although I did just get done reading a long thread on FABO where a troublesome overheating problem was finally fixed by driving the water pump faster...)

I can definitely tell that the Contour fans and shroud are compromising the airflow... and there's not enough radiator efficiency to make up for it.
Unfortunately there is so little room in the front with a big-block that I would have a hard time finding a better fan that will fit in there, nor will a thicker radiator fit without modifying the core support.

Speaking of which, should I cut out the core support on the sides?

I will be looking carefully at the specs for a radiator with two wide tubes (1" will fit but probably not 1.25" tubes).