It doesnt matter how much how much stronger they are if you are just going to put it behind a V6. I would just get the rear axle setup from a 99-04 GT and then have the rear end rebuilt maybe with some 3.73's. That would get your sixer a little more oomph. 3.55 gears are better than your stock ones but still 3.73's will give you more out of the hole. The six needs all the help it can get.