I had to look it up. Your motor's max rpm is 3600 (continuous max is 3400). Cockpit tachometers are notoriously incorrect by 100-200rpm, but when you're below the target by more than that, you are very possibly over propped. It is also possible that your tach is off in the other direction and you're even more over propped than that. Best is to text your wide open throttle rpm under way with a calibrated test tach attached to the motor.I can't swing a larger or higher pitch prop as it would not reach 3200rpm. I forgot to mention I've a 2 blade 15"D x12"P Flex-O-Fold as well. Max it could make is shy of 3300rpm.
You can mail your sample away for an oil analysis. While I think they are good idea, they are more valuable when you do them over time and can see trend lines changing.So far all checks and feels points to rings wear. Compression test seems to confirm that. Anyhow, I'll try the "Warm" and "Wet" test and post results here. Unfortunately, test analysis of crankcase oil isn't common or known here.
Are you seeing any smoke from the exhaust? If your rings are as shot as you suspect, I would expect notable smoking. If so, what color?