Definitely do not go higher than 2 and 1/4 unless you plan on adding tons of hp. GT take-offs are the best bang for the buck for v6ers, you can get them for $130 shipped from midwest mustang. Also there is no need to add an h or x pipe in a v6 because of the fireing order. You can read about it at
www.3.8mustang.com in the bolt ons forum.