Im a lil confused myself. Im sorta pushin towards SLP, but I dont want it too loud, maybe just some flows that Ford puts on, ya know, dont want to void the warranty and all :rollseyes
I have the SLP loudmouths and they are Loud. I love them, but if you are worried about noise, don't get SLP. If you want performance, great quality, and a kick butt sound, go SLP. With the windows up and on the interstate, my cobra with the SLP is much quieter than my 3 chamber flows on my GT. The SLP doesn't have the drone at about 2000 rpms.
I, too, have the SLp loudmouth. I love it and would recommend it to anyone. I posted about it in detail in the new edge cobra forum. It gets 2 big thumbs up from me.