The noise your engine makes is proportional to the power it is making. Ever notice how 90 size engines seem a little louder than 30 size engines.

Bogging = drop in RPM due to the engine struggling with the load it is working against. Remember, the goal is to maintain RPM.

Bogging occurs anytime you apply a load to the engine where the current power output will not be able to maintain RPM. (ie drive your car up hill without adding more power ... the load starts winning and your engine RPM drops). So, to "fix" bogging you have to either decrease pitch/load (ala barracudahockey) or increase power output. If you are at full stick, increasing power output may not be an option since the throttle position will be at or near 100%. Assuming near max throttle, bogging can only be fixed by lowering the pitch/load.

This is why the power and pitch curves must be "tweeked" for best performance from 0% to 100%.