Feets, I'd use the largest straight-through muffler you can fit. The 5" by 11" by 22" Magnaflow or Goerlich Xlerator X141 I think both would be terrific for letting the turbocharged exhaust fly through and getting rid of the noise.

360view: Regarding the back pressure measurements: they will vary greatly depending upon load and gear and engine and car but I can tell you the difference in air flow through the mufflers closed and open is very similar to stock mufflers when closed (around 35% of an open pipe) and around 55 to 60% when open (around that what typical Flowmaster flows when configured with offset offset inlets and outlets). However, please recall that under highway speeds when the throttle is not too far open, the back pressure may not and likely will not be very high no matter what mode the muffler is in. Of course, if the throttle is wide open, the back pressure will be measurably different. If I have my Barracuda out soon, I can measure it one of these days for you.

Tom Hand