ORIGINAL: KeroPower
I just use the OS #6. My Fox .40 R/C runs perfectly on FAI with that plug.
I tried an OS #8 & #6 glow plugs in a couple car engines I had 10 years ago and they ran horrible. The short reach influenced compression to a noticeable degree in my test engine at the time. Traxxas glow plugs ran better. I switched to McCoy 2 years ago and have never looked back since.
So many people put OS on a pedestal, a benchmark if you will, and I just don't see them being that great. I myself won't buy anything with the OS name on it. Especially when their glow plugs are $2-3 more expensive than any other brand sold locally. Their engine prices are outrageous. I'm happy with what I use.