:When you have 550 rwhp, you probably can benefit from a larger diameter exhaust. But for most here at lower hp levels, it's crazy to think there would be such a big difference. They need to be dynoed back-to-back.
Yeah it would be nice to see a back to back dyno if someone is willing to do it. I just have seen both of the exhausts and the first thing that came to my mind was... quicker spoolup. A pipe with bends in it will never beat a straight pipe in air flow.
As for the larger diameter, the only way it would make any difference is if it was a constant diameter after the turbos. If you mix 2.5" downpipes/testpipes with a 3" exhaust your'll most likely hurt the exhaust velocity instead of helping it.