I just got some ultra flo 2.25's welded on for my 2000 gt. It sounds good, but not nearly as loud as I expected them to be, it also took a little while to break them in and they got louder it seems. At idle its really no louder than stock, when you get on the gas it sounds nice and deep, I would like it if they're a little bit louder when I'm cruising at low rpms and at full throttle. All i can tell u is about the Ultra Flo's I've never heard the super 40's. So to break it down, if you want a loud exhaust that is gonna really stand out, dont get the ultra flo's, but if you plan on adding an hpipe or headers and you dont want mufflers that are gonna make it too loud but still have a nice deep sound, go with them.