How many using an A500 overdrive ?

Wow.
I paid 130 from a member here (about what it would have cost me to get one locally) for a low stall version. Looks like there's only 200 rpm difference in stock low vs high stalls. And the high end of the low stall version is the same as the low end of the hi stall version.
Low stall is something like 1600-2000 hi stall is something like 1800-2200 range. Both could theoretically stall at 2000. Though I'm not sure what all influenced that.
Understanding what stall speed is and what effects it is almost as confusing to me as trying to wade thru a cam catalog.