Here's my opinion. Currently my custom stack setup is unfinished, I've just got plain 4" pipe run straight up from the hole I cut in the bed and it ends at the top of the cab. It's quieter than straight 4" was dumped before the axle that's for sure. But it's still loud inside the cab(quad cab) so I've gotta get 2 90 degree elbows and I'm gonna run it up the corner of the bed like most single stacks and I'm gonna use a turn out stack. Unlike most I'm just going with a chrome 4" stack, I think anything bigger than that on a 2500 series truck just looks really out of place, just my opinion of course. I'll post up pics whenever I get time to finish it.