2.5" vs. 3" cat or Y back exhaust?

In a previous post I asked about quiet performance mufflers and pretty much narrowed it down to Dynomax super turbo or Walker quiet flowSS in a large size can, single outlet. My exhaust guy says he'll do either 3" or 2.5" tailpipe w/muffler for $170 but if I want him to wack off the end of the Y and put on a better 2" to 3" collector then do 3" all the way it'd run about $250. Both sound pretty reasonable to me, here's the question for an '04 4.7L 4x4 DAk QC:

With only mods planned being a set of HO cams and moddified TB plumbing to modded air filter box lid(larger) & an sct tune is there really anything to be gained or lost by going to 3" ex. pipe all the way with my few mods? Bottom to midrange is what I would hope to increase. My impression from searching is the general concensus is that the 4.7L engine likes 3" plumbing, is this in all cases, regardless of mods or lack of? Thanks, Mark