TALONTED TURBO,
How long have you had your N1? Mine was really quiet when I first got it and nowadays its quite loud.
Yes it has resonators, but it would sound stupid without them. It has such a nice rumble at idle.
As far a full 3" exhaust goes, unless your O2 housing has a 3" inner diam. why would you need to switch to 3" right at the O2? By keeping the diam. of the exhuast at 2.5" until you pass the flex section, you will keep the exhaust gasses at a constant velocity while they are still hot. Once they get to the "cat back" section of piping they have cooled considerably and a larger pipe may be used without sacraficing velocity.