Okay, I've spent a lot of time wondering where the 2.2hp is going on this motor and I may have figured it out. I'm a little slow!

Since HP is nothing more than TORQUE X RPM, then perhaps the Saito 125 is a very torquey motor that produces most of its power at lower rpm's. Thus, it may spool-up nice and fast, but never rev very high. After all, the max rpm on this motor is 10,000 and many of the smaller Saitos max out around 11,000-12,000.

It may be like trying to compare a car with a Chevy 454 big-block to the same car with a Chevy 350 small-block. The small block will rev higher and produce good HP, while the big block will not rev as high and make most of its power a lower rpm's. What does that mean to the performance of the car? Well, the big block will allow the car to accelerate faster and get up to max speed faster than the small block, but the small block will eventually rev up and reach the same max speed. That's why trucks have lower revving / high-torque motors and cars have higher revving / higher hp motors.

I'm thinking the best application for the 125 would be a heavy 3d or aerobatic plane that needs a lot of low-end power to punch out of a hover. However, it will not outperform a 100 with regard to speed. If you have a lighter airplane, or a plane that you need a lot of speed out of, then the 100 would be a much better choice.

I think the best use of this motor is applications where you have a heavy plane that needs good acceleration. If that's not your application, then the 125 is probably not the best motor..

The biggest benefit of this motor may simply be its ability to accelerate a heavy plane quick.. That's it.