As I understand it, Service Factor is an expression of the relationship between design HP and Total HP. Meaning that a 2 HP motor with a Service Factor of 1.1 can (when pressed) deliver 2.2 HP but is designed to run at 2 HP. A 2 HP motor with a SF of 1.35 can (when pressed) deliver 2.7 HP but is designed to run at 2HP. The higher SF motor has more headroom than one that's closer to 1.0 SF. I could be wrong but I'm pretty sure. Either way, the pump curve will be different for different wet-end combinations and when comparing, the pump curves are more important than motor HP.

In your case, I'd bet that the EcoStar would be able to deliver the same spa action as you've seen to date but also allow you to tailor the flow for other operations. As far as comparing the EcoStar to the Intelliflow, I can't help at all. I bought the EcoStar because I can easily integrate it's onboard control system to my Solar heating controller.