Getting hot on the highway with the AC on.

The more holes that you plug between the radiator support and the engine compartment the more you'll get through the radiator at higher speeds!! If you don't have a radiator support to hood seal it doesn't help at all. There are other places that the air can escape through the radiator support. You can also easily build an air dam below the radiator to force more air through the radiator.
I have also found that the closer that the condenser gets to the radiator the more air flow you get. Best case scenario is to have the condenser dead up against the radiator to cut down on turbulence.