lowest drag for fixed 3 blade?
A German University ran tests a few years ago on several folding and feathering three bladed props. They used a fixed three blade as a control. At 8 knots the fixed prop drag was 420 Newtons locked and 180 free-wheeling. By contrast the better low drag (folding or feathering) props were around 12 Newtons drag. A Newton is around .22 pounds.
The point above is correct about transmissions - some need the input shaft turning for proper lubrication. There is also the noise and wear issue. Always nice to hear that low rumble stop when the prop