I figure a typical 4-2-1 header yields an average of 2-3 additional hp across the entire power pand, and that a 4-1 will yield about 5-6hp or so peak, but only say, 1-2 across the rest of the powerband. These numbers are estimates, but if we use them as an example, then going from a 4-1 back to stock would result in a significant loss in peak power, and probably a 1-2hp or so over the rest of the power band.

If you have 2.25" crush-bent piping, it's probably restricting your exhaust flow about as much as the stock piping would. If you want a quieter exhaust note, while not sacrificing power, get 2.25" mandrel-bent piping with an inline resonator, and run a decent quality straight-thru muffler.