Probably similar to the 4th gen mufflex kits, which you could research and listen to sound clips before deciding. They use magnaflow mufflers, which are very good IMO.
Scale: 1 (quiet)-10 (loud)
Stock = quite (2)
Mufflex 24 = mellow (4)
Mufflex 18 = moderate (7)
Mufflex 14 = loud (9)
Another option a lot of 4th gen guys did was Carven, which has progressive (moderate) or competition (loud).
These are both good drop in replacement options to get rid of the giant, quiet stock muffler. Goring with or without larger 5" tips and leaving your resonators on or cutting those out as will can change sound too. Research if drone is a concern.
Full cat backs don't do much in my research. If youre not going all out with a completely new system front to back, then just muffler replacement is all thats needed, unless the 5th gens have some new restriction point that didn't exist on the 4th gens.