About Cooling:
Copper alone is a better conductor for heat transfer than aluminum. Copper/Brass radiators are generally more effecient at rejecting heat than plane Aluminum. But, Aluminum can be drawn into larger diameter passages giving more surface area for improved cooling despite the setback of a lower thermal conductivity. So given two identically sized radiators - the copper/brass one will cool more effeciently. The major advantages to aluminum are weight savings, manufacturing costs & larger tubing diameters. While I agree that most aftermarket 3-core radiators are a vast improvement over the copper/brass 4-cylinder radiators in the Fox, I would like to point out that there is a 3-core brass radiator available for our cars as well. Now, my car was never supercharged or intercooled, but I did switch over to the 3 core brass radiator and noticed a huge improvement in heat rejection capabilities.
Also, with that being said... All cooling systems are a combination of 3 major components:
1) Air Flow (across the cooling fins)
2) Fan CFM (for in traffic air flow)
3) The radiator itself.
So when you look to improve your cooling system performance, think of all the major factors to get the most bennefit. For example, adding a low pressure zone directly behind the radiator [by use of a vented hood] would create suction at speed. Or add a Mark VIII fan that can pull 3,000+CFM of air without the car moving to help in traffic.
The first link is general magazine information about radiators. The second shows some test results from different radiators.
http://www.chevyhiperformance.com/howto/81658/
http://www.usradiator.com/testing.htm