Mufflers

I have a 2001 GT that just turns me on more every time I drive it and although I'm only a week end driver with this car my wife and I do go on long drives (400 miles last week end). I thinking of putting Ravin or Flowmasters on this pony but a little worried about the cabin noise on a long trip. Does anybody think this may be a problem or will it mellow out at highway speeds in 5th gear?