Are you on a ko3 or a ko4 pudding? The reason I am asking is I have spent a lot of time recently looking into the newer type s3 and golf r(mk6) ic's with the plastic ends and it would seem that ecs spent a bit of time testing both the s3 with Ally ends against the one with plastic ones. They found that by measurements the plastic ended one was approx 20-22% greater volume area than our standard ones and the ally one was around 25%. Flow wise and efficiency were pretty much identical and both were a great improvement over our standard ones. Better still, the plastic ended one meant they didn't require new bolts either.
I have an airtec one fitted to mine (ko3), but I will be swapping it with a mate who has a golf r, as I reckon the airtec is a bit overkill on the ko3, and the golf r one would be better suited.
Just my 2p. Don't know how much they go for compared with the ally ended ones, as I haven't looked.