The secret to quiet with flow is volume (lots of muffler volume). If you are doing custom, go for a 3" muffler in the normal location, another 3" muffler in the rear resonator spot and as big of a resonator in secondary cat location as you can fit. Offset in / center out would quiet it down more than center-in / center-out. A turbo car with three perforated (not louvered) straight through mufflers should be pretty quiet but still flow very well. I have always been partial to magnaflow mufflers when doing custom stuff.
-Charlie