personally, for the 5th gen, i would get an ebay exhaust. a local guy has one and it sounds good to me. other than piping an fitment, the only thing that can go wrong is the muffler breaking apart. well, he had his for a little while and it still sounds pretty good.

but the y pipe on the 3.0 liter maximas has the most restrictions as this is where the pre cats are. replace these instead of full headers and you will save yourself a very big labor fee and money. catback will do you a little good. intake will do you a little good.