Hi Jeff,
It will be obviously less powerful. Also, it will run in the 4-2 mode since it was part of the "S" series. It will be good in a plane that was designed for the old .19 size engines. Not a complete dog, but not up to the modern engines. Definitely not as strong as a .20FP, but very usable in the right size model.
Kinda like comparing an OS .35S with an Aero Tiger .36. The OS .35S is a great stunt engine, but no where near the power of the Aero tiger.
Bill