Is there any documented proof that the alloy is better than the plastic ended ic.
I'm sure you'll find sufficient information if you try a Google search.
I dont think the key issue is with the end caps but mainly with flow rates.
......Id be more concerned about if there is any flow rate difference between the two ic rather than which has what on the ends.
If so remove the IC and install a proper hose. Best flow you can get. No cooling though.
Alloy will actually retain more heat than the plastic.
The most important thing is thermal conductivity. Alloy has a much better TC than any plastic.
That's why you don't find any radiator core made of plastic.
The plastic used on cars is heat resistant and actually has better thermal properties than alloy.
That's complete bullsh*t.
If you touch any plastic plug or loom on a car it will be warm. You touch any alloy part on a car and it will be a lot hotter than the plastic.
And that's why alloy is the (second) best (after copper) material to make radiators.
The only reason why Audi changed to plastic ends is cost savings. VAG use the same
IC on all 2.0 TSI/TFSIs. It's common knowledge the 'old' S3 IC works better though.