so...now that the above posts answered the question....

What plane are you working on? it may help others give suggestions for you.....

it also may take a little experimentation...

I tried several different props on my Zagi with a MEga 16/15 4 brushless motor,,, the 5 x 5 to the 6 x 4 were all within the proper range for amp draw, but I just like the way it flies better with a 5.5 x 4.5 prop......