There is a small program available for you computer that will show you what different size/pitch propellers will do in different cicumstances. As was said above, it figures in the perfect situation but it's a very good tool for determining what different props will do on your plane. You can find it at [link=http://www.bmaps.net/software/thrusthpv20d.zip]Thrust HP[/link]

Hope this helps

Ken