For your streeter;
Is 3 in/3out needed at my 430 hp? No. But big pipes have other advantages. If you don't have to spend more to get them installed. > 3inchers, NOT at WOT, offer;
1) 20% more surface area for cooling the gasses. and
2) 20% more volume ahead of the mufflers, to dump that hot exhaust gas into, so
3) by the time the hot gasses get to the muffs, they have cooled off considerably, and they have condensed into occupying less space, so
4) have lost a lotta energy, so
5) by the time they come out of the end, they are relatively cool, relatively dense, and relatively quiet, having lost their hi-frequency tones . This makes the car pleasant to drive behind. But > 3 inchers for cruising;
6) more importantly; at Part Throttle, while cruising, the engine doesn't even know the pipes are there, and so 30mpgUSg is possible, with the right combo.
7) Furthermore, your headers will run cooler, so the chambers may also run cooler, and be better able to survive running a lil more cylinder pressure. > 3 inchers, at WOT;
with those big pipes, the headers work almost like the pipes are not there;
the inertial tuning of the headers work, and
the scavenging works, and
the overlap cycle works.
and if you tune for it, you don't have to drop them at the track,
and your streeter can run a little less cam, allowing your engine to produce a powerband that works with your transmission, to stay on the pipe, putting down the same or more average power in second gear, and allowing a lower stall. 3inchers for 400hp;
But no, a typical streeter will never NEED the capacity of 3in/3outs. But I have never been sorry I got them. Well, except for the 72 pounds. But No biggie, I ditched the rear seat which nobody ever sits in anyway, and broke even to no system at all.