I ran my SF with its Mac's 10cc long stroke quite pipe again today. This time I surpassed my target rpm of 12,000.

Temp: 67°
Powermaster GMA 5/22
OS #8 plug
APC 11x10
12,128
1.6hp
8.72lbs. static thrust

Calculated prop speed is 99.8mph. This setup is extremely quite. Below 1/2 throttle it's not much louder than a 4-stroke.

David