Thanks for all inputs!

I'll go for the normal/overheat signaling and NTC for a smoother curve.

I think that I won't use LEDs, since I have to use a LCD anyway, to show other informations. something like:

06700 rpm V = 2.45 V
Temp. normal

or maybe just the red LED, much more visible at distance than a few charachters in a LCD.

thank you all!

orlando