Wade, I just looked at the specs for the Saito 100. Horizon states that it puts out 1.8 HP on 30% heli fuel. I am flying mine with a ST90 that supposely puts out 2.5 HP. Personally I beleive that the Saito 100 would fly the Ecstasy. It would certainly hover it, though I am skeptical of it authority of pulling out of a hover. I don't know about you, but I sure as heck don't want to have to buy 30% heli fuel all the time - too expensive. I would much rather buy a bigger motor. I personally would not want a Saito 100 on my Ecstasy. I would go with the Saito 120 though. I am sure that you are asking because you probably have a Saito 100 already. IMHO, I would look for a different aircraft for that Saito 100. You can purchase a ST90 from Tower for under $150. I love mine.
Sorry I couldn't give you a better home for your Saito 100, but I hate to see anyone puchase and build one of my designs and not be happy with it.
Take Care & Happy Holidays!
Kevin