10X8 is a heavy load for any .40.... 10X7 is normal for a .46.

For trainers I recommend 11X4 or 11X5 on a .40. The larger dia and lower pitch helps you have the pull at low airspeed to get out of trouble. The low pitch also helps in slowing down for landing

11 X 4 is ideal for a 4*40... they stick on the ground instead of floatng on past the runway with the engine idleing which is a common complaint with a 10X6. Vertical climb is improved with the low pitch prop too. A .46 0n the 4*40 and the APC 12.25X3.75... unlimited vertical. .40 and 11X4... infinite inside-outside vertical 8's (not quite unlimited vertical climb, but close)

3 blade props at high rpm are very inefficient.. the blade are flying in each other's turbulence unles the plane is moving along fast... problem is, you'll have trouble building up the speed. Glow engines just tend to operate at too high an rpm for 3 blade props to work well. (they look cool, and people mostly use them for a more scale appearance)

If you ever try a ducted fan... remember that you have to build up some airspeed to get decent thrust out of the thing. full throttle and nose high at stall speed, you'll NEVER build speed. the fan blades will be stalled (props are just wings moving in circles) gain a bit more airspeed before lift-off and the thing'll fly like a different airplane. Same idea as the 3 blade prop... just a more dramatic difference.