I should have mentioned that what I read on is 05+ and that section is where I read this.

Here is one where someone was asking and got answers that all said that axle back exhaust doesn't really gain anything
http://www.mustangforums.com/m_1353449/tm.htm

There are a few more. For earlier mustangs there could be a noticeable change, but wouldn't know.

 

Thanks.