hey man, i have the SLP LM1 with SLP catted x-pipe. click on the link in my sig to see some short vids.
i just ordered the LM2 muffs and they would have been here today if the dumbasses i ordered them from knew the difference between Pennsylvania and Arkansas
anyway, i highly reccomend the SLP modular system. like some of the guys said, its high quality, mandrel bent stainless steel, and you can swap out between three different muffs/resonators.
check out this link, scroll half way down, and it will show you the difference between the LMI, LMII and Powerflo. the LM1 will be the loudest, and a little raspier than the LMII. you will definitely turn heads with it. the LM2 is a bit more reserved than the LMI, but still quite loud, and not as raspy as the LMI. The poweflo's i havent heard in person, but ive been told they are still loud (not as loud as the LM's) and somewhat comparable to flow's, but dont have the drone that flow's do. thats just what ive been told though.
http://www.rpmoutlet.com/musv8mag.htm
anyway, here's another link with vids of a guy with the LMII's and stock h-pipe. just remember, when you install an aftermarked mid-pipe, (preferably a catted X with the LMI) it will really open up the exhaust.
http://www.putfile.com/blue2kmustanggt
good luck in deciding