Seeing minimal gains (10whp) on Ray's car, from stock to the DNP kit, I don't think it's that beneficial to go oversized, I know the math says otherwise.
On another note, I've got a CX side mount hard pipe kit on my car and it's garbage in the fitment department, though it was their first release, years ago. But looking at it, I believe it could be modified to fit better and possibly bring that front cross-over pipe that goes over the exhaust manifold, to go under, though, after looking, I'm not sure how much gains would be had as it'll be close to the downpipe/precat although airflow might be better in that area.
Here's what I found for reference on the ETS kit.
Attachment 7047
You could do a similar routing to this, but come off the drivers side cooler exit and up past the front turbo to the Y-pipe. The difference here is the fact that the ETS kit runs near the hot exhaust BEFORE the intercooler, where as on the side mount setup, it would be AFTER the intercooler, so I don't know if there's as much of a benefit to cooling performance as I thought.

