I went to the LHS to pick up a colder glow plug. I explained to him why I need it. He ended up talking me out of it, explaining why it wouldn't work for what I want to do. He gave a couple reason's:

1) 4-stroke engines (like the one in question, RCV 90SP) needs HOT glow plugs to keep the filament lit up for all four strokes of the piston. A cooler plug would lose it's glow between ignitions.
2) Cooler glow plugs are used in 2-stroke engines for high performance applications, like racing. It wouldn't work to put in a cooler glow plug and just lazily fly around.

I'm going to try lower nitro after my current jug of fuel is done.

For now, I'm trying to get my head around this peak RPM thing. How can I find it? My propeller is custom made and I do actually have the ability to adjust the pitch (on the ground only). I have some RPM numbers at various pitch settings. Can anything be determined from these numbers?...

18x13, 3840 RPM
18x11, 4400 RPM
18x10, 4450 RPM

16x13, 4760 RPM
16x12, 4960 RPM
16x11, 5200 RPM

The typical RPM for this engine is between 5000 and 5400 RPM. This number is about half of a typical engine because it has built-in 2:1 gear reduction.

Juice