I had a 4" straight through Dynomax muffler, when I deleted it, there wasn't as much change as I thought there would be. My biggest sound gains were in dumping the resonator (cat was gone when I bought it). If I had to do it again, I'd get this set up from MBRP and be done with it. No cat, no muffler, no problem!
MBRP Performance Exhaust