The main differance is the non ringed or ABC type engine has a tappered cylinder giving high compression at the top of the stroke, the ringed engine has a constant bore cylinder , this is the main reason for the power differance, in some ringed engines the Piston may be Steel vs Aluminium in the ABC type engine, the lighter piston can be ran at higher rpm. The cylinder in the ringed engine may also be steel vs Nickle or Chrome, not quite as friction free.

the ringed engine can be more consistant in tempature changes, going from running in cold weather will not effect starting as much as a non-ringed , a ringed engine is cheaper to renew compression and is less suseptable to damage from dirt or forign matter in the engine sence the ring can skip over or just push it on threw . The ring can also be damaged quicker by overlean runs because of the lack of Lube.

I personnely see the ringed engine as being more consistant, and longer lasting .

The ABC can develope more power, but I haven't seen the 2000 rpm differance , this can greatly depend on the prop being used.

The only thing you can compare side by side is the ringed and non ringed of the same model, don't compare the FX with a SF or FSR , differant models have differant porting as well which can give higher rpm for a given size engine.

The .46 SF came in ringed and nonringed, the power advantage with the ABC engine was not that noticable IMO. I still have the ringed engine, almost worn out it still turns a 10X7 around 14,000 rpm.