At what power do you need a 5" exhuast, I plain to stay around 350 to the ground. Will a 5" lower my egts pulling or is the 4" the best for me? I'm also putting the new up pipe on and a plug in the egr cooler, leaven the cool in.
i asked the same thing and all i can say is im glad i went with the 5" ive had it on for about a month now and love it, to me 4" systems on a 6L sound a little raspy for my taste where the 5" has a nice super deep tone to it. as far as performance i dont think your gaining any over the 4" its more of a sound difference than anything.
my system was the diamond eye kit you can get them on ebay but my old boss is a dealer for them so i got a good deal this is why i chose the kit. i had to make a piece to go where they wanted you to put the cat back on but i think you can buy it with the cat delete piece either way it wasnt a big deal. my truck has a c-channel fith wheel plate and it doesnt even come close to hitting it. where it gets kinda tight is between the shock and the spare tire but there is no hitting or rubbing and i must say it sounds just flat out amazing im very happy with it.