When you say nice cruise you are basing this on what you see. Well that's ground speed. Airspeed we can't measure. Stall speed is based on airspeed. Just be careful you don't get too slow of an airspeed and stall.
The way you make it sound it sounds like your throttle isn't set up correctly. The engine should increase in speed the full range of throttle movement.
The 13x6 should be just fine but Master Airscrew have a lot of flex to them try and APC prop