Here in the UK at sea level the following works well:
5% nitro
14x4w APC prop.
Irvine .72
BCM exhaust
C/G @ 6"
AUW 5.75LBS

Running rich, I get about 10.500 rpm which gives between 9.5 and 10 lbs thrust.
Out of sight vertical from the hover.

Cheap engine / cheap fuel / awesome performance.

Good luck with the GMS. Simon. Dorset UK.