Performance wise I doubt that any of us could tell much difference. In the old days a ringed engine would hold it's compression longer than an ABC, but the new metals used seem to have cured that with ABC's. The real difference is that a ringed engine will take a lot longer to break in because you will have to give time for the ring to set. Also a lean run early in the life of a ringed engine is the kiss of death. I would say that in the size you are considering, an ABC will be more user friendly.