Rapid has some good questions. It is not always the radiator itself. Aluminum only cools a tiny bit better than brass... a tiny bit. I has more to do with the entire package; how many rows, how large are the tubes, how many tubes per row, how much air is pulled through, etc. and bigger is not always better.

For example, if you had a 1000-row radiator, it would be too hard for air to flow through. If you had 50 electric fans, they would block highway air flow where you don't need a fan...etc, etc.

You're trying to get heat from the cylinders into the coolant, then into the radiator, then out into the outside air.

So, what is your exact "runs hot" situation?