Good thread!
I will just add that HP ratings are total BS. You have a HP rating for the motor operating without a pump on it. Then you have the motor but put on larger impeller and report it as the larger number. And as stated, none of this takes into account the amount of plumbing, type of jets, is there a diverter valve? Diverter valves rob up to 18% of the power (I have read). Every inch of plumbing, every 90 degree elbow, etc, reduce pressure by friction.
As said above, don't even look at what the manufacturer says the HP is. Feel the pressure from the jets. Does it feel strong enough? Great, who cares what HP someone says it is.