A 11x7 flies a lot better . Aviastar engines focus on torque rather than high RPM. Shoot for about 10500~11000RPM on the ground. Too high RPM without enough oil will hurt the engine.
In the old days when we flew pattern, a 11x7 is already the prop for a 60~61.
As for Sig glow plugs, I 've used all three of them and they all worked fine ( depends on the nitro content of your fuel)
Currently I am using 15% nitro.
Merlin glow plugs are made in the USA. Here is their web site:
http://www.merlinglowplugs.biz/