COntrary to what people think they know about Nitro.....
Higher NItro, means a COOLER runnig ENGINE....

One of the RC care mags did a entire workings of it.....
Simply.:
Higher nitro= richer setting to offset the increased oxygen
richer needle means more fuel run through the engine (nitro, oils, alcohol)
='s cooler running engine.....

Now, extra stress on the engine? That is a different story.....

The colder plug is used to offset the increased TIMING associated with the HIgher combustion properties of the
higher percentages of NItro/oxygen..

Too hot and you get KNOCK (The fuel, ignites when the pistion is going on it's down stroke or just comming on it's way up)
Depends on how much the timming has advanced
...... If it isn't KNOCKING..... and there isn't any pitting in on the inside of the head of the engine,
and you are not burning out glow filiments regularly you should be just fine!....

Justin