According to this thrust chart, you need to be turning 8000 RPM with a 20x6 prop on that Moki to get 19# of thrust. Keep in mind that this chart is an average prop. All different mfg props are a little more/less load even though they are all labled as 20x6. Also they are all different efficiencies, APC being the best, but also the heaviest (not good for spool up).

http://www.zingerpropeller.com/Thrust.htm

My Moki 1.80 and Bambula 18x8 prop can hover a 15 lb CAP232, includes a full tank of fuel, at half throttle so I'd imagine that I'm getting around 17-19 lbs of static thrust. I'd say the previous poster's guess is pretty good.