Really can't say much about the alum. radiator, but it's the water that does the cooling. Water is an amazing heat sink. Just try soldering pipe that has a couple drops in it. It just can't be done till the water is gone. I don't believe it makes a dern bit of difference what the radiator is made out of as long as it's metal - as far as cooling is concerned anyway. If the aluminum one has plastic tops and bottoms (presumably b/c it can't be soldered, therefore can't be repaired either) I'd listen to BJ and stay far away. Just my .02

Also, I thought aluminum blocks are for weight, not heat. But I've been wrong plenty times.