Theres an audible difference between the two but not a major one. I think mac sounds better than my old flows did. I believe mac flows better than flowmasters but you wouldn't feel it on the butt dyno. I'd get a sound clip of my car if I could, the only difference being you have an h-pipe and I have an x-pipe but it would give a better idea. Since my camera is ******* I can't even give you pics of my tailpipes. There a little bigger than the 2.5" pipes so I'd assume there 3". There bigger than stock but there not fart cannons out back either, I personally think they look good. How much is he asking for the exhaust? I wouldn't mess with it unless it's dirt cheap, exhause can be a bitch to line back up and keep from rattling.