ORIGINAL: bkdavy

If your plane is fast, but has poor vertical performance and long takeoff runs, decrease pitch and increase diameter (go one number on each). This will increase your static thrust, but you will sacrifice speed. If your plane has great vertical performance, but you want to go faster, decrease prop diameter and increase pitch (again one number on each). Your plane will fly faster in straight and level flight, but will not climb vertically as well. You will also take longer to reduce speed on landing approaches.

Hope this helps.
Brad