Unless you are competitively racing, or going for dyno numbers you header and exhaust choice of 4"1, tri-y, dual 2.5/3 or even single 3.5/4.0" is mute, or really, the opposite of mute, because it's really all about the sound, and legalities
I'm currently swapping out some Pacemaker tri-y headers for some 1 7/8 ceramic coated mild steel 4:1, because in my opinion, the mild steel long tube 4:1 sound better than the mild steel 1 5/8 tri-y
My system will consists of 1 7/8 long tube 4:1 with a 3" flange reduced to the current dual 200 cell 2.5" front pipes merged into a 3.5", with a large resonator in the mid pipe, and a large offset muffler at the rear
I'm also not a fan of stainless headers, or exhausts, unless they are 321
I find that I don't like the "tone" that cheap 304 stainless exhaust makes
I also like the cheap ability of chopping and changing a mild steel exhaust, if you start with medium sized resonators and mufflers it costs bugger all to swap them out for larger or smaller to "tune" the sound to your preference
My neighbour recently spent around $4k on a full stainless headers and 3" exhaust on his VF SS which now drones like 10 droney things and wirh the windows up is verging on psychological damage (his missus has said "fix it"), and no, that $4k didn't even cover ceramic coating the headers
If there's only 1 thing you take from my ramblings, get some good ceramic coating done to whatever style and size headers you get prior to installation