dude hands down slp is the best for sound and tops in quality for the money.borla is also good but way overpriced,MAGNA FLOW IS ALSO GOOD BUT THE TIPS LOOK LIKE ASS.slp tips are the best out there no question.flowmaster.............dont even think about that garbage unless you have a 5.0.and mac.well i dont know to much on mac exhaust from modualr standards i know the sound is always badass but the qualty is horendous.as far as the gains you will typically gain 5-10 hp with any of those applications.if you do get slp make sure you get the xpipe with cats this combo is probably good for atleast 20hp
SLP LM1's may sound ok with cats, but they sound like the ass with and O/R midpipe.
I have a pair that I took off until I get cats put in my O/R prochamber
Love the LMI , but keeps the cats. I found out the hard way when i tried an o/r x pipe with it. SOunded like complete crap. But on the stock midpipe , it's great.