Only 850 degrees fahrenheit? That seems awfully low. I used to race karts (yamaha 100cc piston port) years ago, and we shot for 1250 degrees F. I had a 400HP Subaru WRX. When tuning I shot for EGTs in the 1450 - 1500 degree range. Some guys liked to run as high a 1600. I also used to race in the SCCA Formula 500 class. On a 500CC rotax we were running about 1300 degrees.

I've stuck a few 2-stroke pistons in my day, but never under 1400 degrees. In all my experience with EGTs, wide open throttle at 850 degrees would be pig rich.

I trust that you know that you stick pistons at 900 degrees. But now you have me curious as to whether your particular thermocouple reads low, or RC engines really run that cold.