Well Izzy is a therapy doggie as well with Delta and she is so laid back (unless she sees kitty cats..lol). I sort of knew by her temperment that she would be a good therapy dog so we went with it. I tried agility with Izzy and though she loved it she was taking her goodie ol' time going from one event to the other.
I could have lit a fire cracker under her and she still would take her good old time..though she was not afraid of the full size equipment including the a-frame and ramp.
Now Cosmo has sooo much energy and can run and leap so I know he would not be calm for therapy but I'm going to try him later for agility and see how that goes. That dog can fly.
I guess you can tell when you see the pups in action at the breeders to see how they relate to each other and run around.