FlyingStone
You are correct, I don't think you can ruin an engine at power check RPM but depending on how much you've leaned the mixture it will start pinking. If it's a long taxi (not usually at my home base, but at my old airport it was a very long taxi) then I'll have the mixture back pretty far.
Interesting info on ROP/LOP, quite (most) often the problem is that the mixture isn't the same for all cylinders, so you end up having to compromise and often that leaves you running ROP, however if its possible to run 50 LOP it's a good idea. Also cockpit instrumentation is a problem - the most many of us have to go on is an EGT, but more often than not there isn't even that, I have to lean using just the tacho because in the aircraft I fly that's all there is, so its ROP for me. But if you've got the instrumentation...