Highly unlikely that the starter operating voltage had anything to do with the damaged flywheel. The starter drive should be fully engaged with the ring gear teeth on the flywheel before the starter begins spinning (either at high speed or low speed). If the starter motor is misaligned with the flywheel (loose bolts or improperly shimmed)then tooth damage can easily occur.
I have no idea what type engine you have? 216 I am guessing?
Make sure that the starter drive is the correct match for your ring gear (number of teeth per inch)the 235 and 216 starter drives are different and not inter changable even though the starter will mount up to the bell housing.
6 to 12 preference? makes little to no difference, starters are not that picky about volts, but draw a high amperage.

Best Regards
Will