I have an SBC and went with factory manifolds, (get this) a catalytic converter and Dynomax muffler - single 2.5" exhaust. The Jeep is relatively quiet at idle and sounds like a Corvette at WOT. The builder talked me into a high-flow cat' - saying it helps to clean up the fumes and smell of the exhaust. Originally, I thought I wanted headers and duals - for power. But man... I don't know what I'd do with more power. On the street, the Jeep will spin or bark the tires in any gear - literally, if I'm coasting in 4th gear and stomp it, it'll bark the 35s. I assume part of that is the fuel injected motor - quick throttle response, etc. But the 2.5" pipe sure doesn't feel like it's holdin it back.
1981 CJ8, Chevy 5.7, SM465, D300, RE 4.5, 35" BFG MTs, 20/30 4.56, Detroits, Warn 9500ti