Good info fellas.

Dave, Thats what Im planning to do if I stick with the 3.5" collector run 3.5" pipe to the mufflers then after the mufflers when the gases have cooled sufficiently, step down to 3" over the rear end then another pair of 3" in/out mufflers at the rear of the car for further noise control as I have the space. I may also experiment with alum tubing and possible oval tubing and use electric cutouts to further reduce the noise if reqd.

Here's food for thought, I just confirmed with my dyno guy, the combo made 850HP at 6300rpm and 770TQ at 5300rpm with 2 1/8" Dyno headers with a 3.5" collector

Interesting.