Both of those props seem to me to be a bit much for the engine in question. Will they hurt it? No. It will require a higher idle speed due to the extra load on the engine as opposed to using a 10x6 or so. At about $3-$4 a prop for Master Airscrew get a few different sizes and experiment with them untill you come up with a combination YOU like and that may just be that 12.25x3.75 you have. As far as I know APC is the only producer of that size prop and it was desinged for the .46 Fx/Ax and similarilly powered engines (TT .46, etc.) for 40 size 3D planes. Thus it costs more than the afor mentioned MAS props.