Thank you for the explanation, Jason.
I emailed the builder to ask about the Whisperflo size spec and this was her response:
"That is determined by the county...based on gpm, size of plumbing distance from pump and spec on pump"
I thought that was a little odd, since she was out here to do the estimate, but maybe that's a normal response to such as question?
In any case, with a pool as tiny as the one we're planning on, and the fact that the pump equipment will be maybe 12 feet from the pool, seems like your 1HP Superflo two-speed is a good solution.