Oh purely with the window down, with it up it amazes me that you really can't hear any difference at any speed. I had a 3 1/2 inch pipe put in, no BTM for me. As for the local muffler shop that only has 3" pipe, they are right that it won't make a super huge difference but it could make it sound different and it will effect flow somewhat. IMO, it would be silly to have them put 3" in there, if I were you I would hold out and find a shop that has the bigger stuff. My wife drives the truck more than I do, it's our family 'dog-mobile' and she has no issues with the way it sounds at all. Best of luck!
SCott