alatriste, LOMCEVAK,
Your both right on. It is only for close in monitors that the Flaps 20 is better for takeoff due to noise abatement. The takeoff roll is longer at Flaps 10 and forces the airplane to leave the ground so close to the monitors that you are still at full power as you cross over. The flaps 20 allows you to leave the ground earlier and slower, thus allowing you to obtain sufficient altitude so that you can power back just before reaching the monitor.
I have designed climb profiles that call for a flaps 10 with a slow decel from V2 +20 to V2 + 10 after you reach ~500ft that gets you much better monitor levels even at close in monitors, but alas certain safety issues arise. You want the best noise levels at any monitor at any airport, cutback to MAX CRUISE and climb to 3000 ft and then go to MAX climb and you will see about a 3-4 dB drop on 747s.
