Iagree with you D. This is the best guide I've found and use for Ideal temp search.

What is the ideal engine temperature?

There is no IDEAL temperature for any engine. There are many variables that affect it; Ambient temp, fuel type and nitro content, altitude & barometric pressure, Pipe/manifold type and setting, clutch setting, glow-plug, gear ratio, available traction, How hard your driving, on road or off road Etc. Etc.

All of the following conditions MUST be met before any temperature can be considered correct, assuming the engine is in good shape.
1.-There must be a visible trail of smoke when accelerating from EVERY corner.
2.-The idle is stable.
3.-The glow plug wire stays somewhat shiny and the coil stays round (UN - DISTORTED).
4.-The performance is good.

To know if your engine is properly tuned, you should learn how to read a plug:
1.- Wire and surrounding bottom of plug wet, with like new shiny wire = Rich side of optimum power 85%
2.-Wire and surrounding bottom of plug starting to dry and wire starting to gray = Very close to optimum power 95%
3.-Wire and surrounding bottom of plug dry, wire totally gray but not distorted = Optimum power 100%
4.-Wire and surrounding bottom of plug dry, wire distorted = Slightly lean DANGER!
5.-Wire and surrounding bottom of plug dry, wire broken and distorted or burnt up = Extremely lean POSSIBLE ENGINE DAMAGE!

Actually when a new plug wire just goes slightly gray after a 5 or 10 minute hard run it means your very close to an optimal horsepower tune, but be careful the next step is TOO LEAN!

Note: You can only "Read" your plug in a nearly new state (Wire like new and shiny). A gray plug can still operate well. But after it has totally gone gray performance can start to fall off. To test just put in a new plug and if there is no difference in performance save the gray one or put it back in. If your engine does not feel or run right try a new plug before making major tune change's

AFM