Nitro,
First, welcome. Second, hit your "Caplock" key. No one likes yelling.

Props have two numbers, diameter and pitch. Diameter is the first number on the prop; 10", 11", etc. Pitch is the second number.

It's the pitch that produces speed, the diameter produces thrust (or vertical pull).

General rule of thumb. If you increase diameter by 1", you must decrease pitch by the same amount. In other words, a 9X8 is similar to a 10X7 and an 11X6. Thrust and speed change, but they have about the same impact on the engines ability to spin them. Keep in mind, this is a very general rule of thumb. I wouldn't recommend trying a 7X10 on that 46, or a 13X4.

If you want speed, increase the pitch. A 10 X 6 will produce higher spped, but less thrust than an 11 X 5. You'll have to play around with props to find the one you like and performs best with your engine.

If it's an OS 46LA, I'd say start with a 10X6. If it's an FX, try a 10X7 or 11X6.

Good luck,
Dennis-