I have an OS 65 LA in an kangke su 26 profile weight is 5.25 pounds with a heavy metal gear servo in the tail for the rudder and a 6 volt pack. Kept the standard 6 ounce tank. The engine spins a 14x 4 Xoar wood prop at 10,000 rpms with a great idle and a nice transition. The xoar transits better than a heavier APC 14x 4 wide. Fuel economy is great with 10 to 12 minutes on average.

I would not compare this to a 45 power wise because it obviously should and does have a lot more torque. I chose it so I would not have to spring another 100 bucks for a 4 stroke of similar weight/power (it’s a bit heavy but the short nose makes it a great balancing tool!).

It certainly does not have the broad power range of a 4 stroke but it spins the big props on a small 3 d profile with no problems.
Contrary to what has been written in this thread I have not found bushed engines to require a lot of care- quite the opposite. I have some old FP 40’s that still run flawlessly after 20 years.

The only thing is you can't “re bush” the engines cheaply so once they are done they are done. I run mine between 18 and 20% oil 10% nitro. I do agree they are not powerhouses and would keep them in lighter planes that need big props to perform or trainer types. That is the perfect application for them. And of course its nice to spin a big prop with good fuel economy.
I love this combo for a 40 to 50 size profile and am building another one exactly the same!
I am also going to try a 65 AX which is lighter and more powerful and fits the “super muffler” as well in a 3rd kangke su 26.

Have fun!