Those revs are just fine - actually the engine heat is likely less than those loaded to 6100
revs don't hurt these engines
I turn my ZDZ's (basically identical inside ) over 8000- no problems
I turn my MVVS 1.6 -over 10000- runs like a fine watch
the trick is heat control and good oils
I don't run around with these engines wide open for a whole flight revving like this - these model engines are expected to run at various speeds during a flight
on a good exhaust system that 6800 does not sound unreasonable