By reading the Saito specs posted by The Ghost you will note that this particular engine is intended to run with a prop range from 11 x 8 to 12 x 8 so definitively you are running with a lower end prop.
Many engines run different but your goal, as has been mentioned is to have a peak near 9,500 rpm. so you will need to find the right prop that will give this numbers (best torque of the engine).
I would try a 12 x 7 which is with in the range and is not much bigger than the one that you are using already.
Also keep in mind that many 4 stroke companies will suggest to break in a new engine with a lower end prop. just like you did, but as you are reaching the higher RPM numbers that the engine is able to give, you will want to select another prop. to stay in the operating range.

Regards.
Alfred.