I do realize that pump can operate at any speed. However the thing I would be concerned about is the electronic complexity of the thing. A two speed motor is just another set of windings and a switch but when you get into continuously variable speed motors you have a lot of electronics involved and it operates in a relatively harsh environment to boot. Granted the reliability of the electronics has gotten very good, especially in the automotive underhood environment which is extremely harsh from a thermal standpoint. However, the pool environment is harsh in some ways too, namely power line spikes and lightening. I also realize there are lots of electronics in the home today that survive spikes quite well. Just my comments. I believe simpler is better. I think once you get to know your pool you can settle in on runtimes and speeds that will work no matter what the math says.
Al