Just been researching the differences on various american forums and they report no difference in the cooling characteristics as the core is the same and no impeded flow.
My point about the plastic end caps is that they will not absorb heat as much as the aluminium (not alloy) end ic when driving slowly in town traffic. I know plastic wont cool air flow but it wont allow it to get warmer than metal would either. Thats why they dont make air boxes out of metal, as they would just be a big heat sink with engine temps.
Mk.V airboxes are placed inside the warm engine bay. The IC is placed in front of the radiator.
It's only job is to cool air. So it does make sense to make it from a material of proper thermal
conductivity. That's why the core is alloy. That's why high grade ICs are made of alloy com-
pletely. There is no advantage on plastic other than cost savings. Have a look at APR, Forge
or THS ICs. They have alloy ends. Audi won't have made the old S3 IC full alloy if there would
no advantage. It's nothing new they make things worse to save some cents.