If you compare Brison 3.2 (52.5cc) with the 43cc (2.6) engine, that is a bit apples and pears, but it shows how strong the little one realy is.
Running less oil will not bring you one single rpm extra. Probably less.

When using the 3xM5 bolts only, check them before each flight for tightness. If you allow the bolts to take shear forces, you <will> loose the prop sooner or later. I would rather use the single M10x1+contra-nut only on wood propellers. For security, I add just two of the three M5 bolts, and torque them lightly.