I agree with your post above Griz, but will add a few things.
Yes the F800GS will compensate for a more free intake and exhaust to a point. It does have an oxygen sensor and a learning fuel map.
Base idle and closed throttle decel are NOT compensated by the F800GS but rather on a fixed fuel map.
All of them pop some on decel and this is much louder with aftermarket exhausts at least partially because the exhaust noises are usually much less muffled.
If power is all that one cares about then lambda (14.7 : 1 by mass) is not what you are looking for, you are looking for a somewhat fuel rich mixture.
This will be helpful to exhaust valves, tend to foul spark plugs, suck from a hydrocarbon and carbon monoxide emissions standpoint, destroy the cat, and reduce fuel economy, but will increase HP slightly
Owned to date. Honda Aero 50, Honda Elite 80, Honda Elite 250x2, Suzuki Katana, Suzuki RF600, Yamaha YZF1000R, Kymco Xciting 500, Suzuki GS500, Suzuki Burgman 650, BMW F800GSx2, BMW S1000RR, Aprilia Scarabeo 200, Aprilia Caponord, Aprilia Sportcity 250
I love and miss you Jeneca and I'm sorry.