Buzzerd,
I always lean my Cessna 150, unless staying in the circuit. I lean with reference to the digital EGT. I lean so as to be about 50 rich of peak on the leanest cylinder. You can go more lean, though at higher power settings I'm not so happy with the extreme temperatures to which the entire exhaust system will be subjected. It is possible to damage the muffler with very high EGT's (ask me how I know!). I run at 2500 RPM, as that is the engine speed at which the mixture at each of the cylinders is the closest to ideal. At higher or lower power settings, the mixture distribution is much less even. It is possible to run lean of peak, though I would only do this in situations of dire need to increase endurance. The small increase in endurance could come at quite a cost in exhaust valve/ exhaust damage. As said, I run at 2500RPM unless some circumstance dictates otherwise. You can easily expect 3500 to 4000 hours between overhauls for a well cared for O-200, though expect to have at lease one set of cyilnders replaced during that time. I run Mogas nearly exclusively, and credit the lead free fuel with preventing lead fouling and other unhappy engine events. I have never had a problem which I attributed to the use of Mogas.
I overhauled my engine at 3750 hours since the previous overhaul. I did this only because I found metal in the oil filter. It turned out to be shavings from the crimped on alternator drive coupling (which would only have required removal of the alternator, but I did not know that). The engine was otherwise in excellent condition. The only thing which was non-conforming, was wear on one crankshaft journal which was .0008" undersized in one dimension only. I had the crank ground 10 under, and it will serve me as long as I fly. I have had the 1975 150M for 21 years, during which I have flown it 2660 hours. I could not be happier with it!
I hope this helps.
Pilot DAR