Yup. U hit it. To give you an idea, my GN at 30psi had almost the exact same pressure in the exhaust mani. 6176 turbonetics turbo...76mm hot side with a .63 AR for spooling. That was a 3" single shot down pipe and exhaust on 3.8 with stock heads.
The .82 AR isn't going to help much. A single turbo is still a good choice. But IMO, 76mm. And with a turbo that big you want the exhaust wheel that size minimum and never neck down. So 3" to a dual 3" catback would be fine. Even 3" to a dual 2.5" catback would be ok. You have to use some type of straight through no back pressure muffler.
It would be worth your time calling precision turbo and seeing by chance if Patrick still works there. If not get one of the other techs and tell them what your are turbocharging and what your goals are. They don't have a kit, but they will tell you proper snail size.
2014 GMC CC Z71
2010 Camaro 2ss/rs---SOLD 4/15/14
-654whp with a few cosmetic things, Pfadt suspension, Vortech, CircleD, GPI ss3 vvt bump stick, gears, stuff in between,18" TSW N'rings for drag duty, 20" Forgestar F14s for street.
rhino@ Gwatney Chevrolet/GPI Jacksonville AR
TCAudio in Benton AR