I didn't get the PP. I don't like the black painted wheels that come with it. Mine came with better looking wheels (19 inch) IMHO. I drove a Mustang with a PP and without and I couldn't tell the difference other than it's a little stiffer in the turns. But as far as overall performance I didn't...
Tune at your own risk.... if there is a problem and Ford declares that the problem is as a result of you retuning the engine they will not cover the repair and will void your warranty.
for more info read here...
http://www.mustang6g.com/forums/showthread.php?t=10970