Unfortunately I don't have to an apples to apples comparison. I tried out a 3" flow master turn down exhaust but soon after I made my AFE 2.5 exhaust into a turn down at this time and swapped back to smaller diameter piping. At idle rpm there is no noticeable difference. There's more throaty/raspiness on revving and WOT. Noticeable in cab? About the same as before. I think what changed the exhaust tone and loudness was the piping diameter and muffler design. Fwiw, I'll be going back to 3" after I weld on an additional resonator.
I found these JBAs locally with GM cat converters welded on. Installation would be time consuming test fitting several times and tacking the connections in place but I feel confident that I could do it myself with the amount of space available. No CELs related to the header install. Though what I do know now about catalytic converters, there's no way to avoid properly warming up before romping on it. You will get CEL without consideration to warm up times unless you disable the converters completely.
