LA, i am far from an expert tuner like mike, but u may benefit from my personal experience.
i installed a free flow cat back exhaust, same as the HKS japenese gear, but locally built.
i had it dynod before the tune for a baseline, this was after adding the cat back twin cannon exhaust.
what happened was the flow was so much better from stock that the mitsu comp compensated by adding more boost, which was very nice (give me G`sss)
but it tapered off at higher revs and was a narrow boost band.
after the tune i have much more power over the whole rev range, to the tune of 50hp at the wheels from stock.
so your call, thats how the mods u are planning on affected my performance.
i reiterate, this is only anectdotal evidence, and mike can probably explain it better for u and me?
BB.
just my 2 cents worth.
P.S i also added a k&n free flow air filter, for the intake side of the booster.
PPS. my exhaust initially sounde like shit, it sounded like there was a hole in the muffler and the drone inside the cabin was unbearable at 100k`s. (i like a quiet acheiver)instead of the effortless silence of the restrictive stock pipes i had a monster.
so my favourite performance exhaust guy said that he could fix it and tacked a coupla inserts inside said cannons.
jeezus, u wouldnt believe the difference, it puuuuurs man, now mike will probably say that i have lost a coupla hp, but hey, i`m 58 and in my second childhood,
i crave serenity at 100 mph.