I do have dual exhuast , the pipework is 2.5 inches. It gave me a real kick. I'm not technically inclined in the Exhuast dept but I do know some back pressure is good, and that your engine can only send out what it takes in. I'd say 2.5 just because that's all I ever hear about on these forums..but hey, all you custom single exhaust guys should start speaking up you true sleepers!
