So ever the voice of reason...
I somehow doubt that we're smarter than dozens of German engineers in these matters.
Every review I've read of the aftermarket exhausts shows either degraded performance or tiny improvements at only certain parts of the power curve. I don't need noise on my bike, either, I perfer stealth and speed.
And if a simple chip swap would improve mileage and performance, I think they would have done this - the motorcycle market is very competitive and being able to claim a few more horsepower is quite important.
This reminds me the the guys who would take their new pickups to the tire store to have lift kits and oversized wheels and tires installed 'to improve the handling'.