In 3D flying the Saito 72 way out performs the OS 70 because you can use 30% helicopter fuel in the Saito and it responds well to it without any harm. YS engines benefit greatly from 20 to 30% fuel also.

On the subject of fuel consumption, keep in mind that more horsepower does not come for free. The laws of physics don't allow it.

Saitos tend to be lighter. 3D fliers are very weight sensitive people while scale war bird people don't seem to mind a little extra weight.

4-stroke engines have a crankcase vent which can be piped overboard with a piece of fuel tubing but I've never seen much of anything coming out of there anyway. Pumped 4-strokes like the YS are completely sealed and have no leakage unless something is wrong with them.

For displacement, the YS is the most powerful.