By engine loading are you referring to the prop size?

If that is what you are asking, it depends on the engine, fuel, and what type plane you need to prop. Many seem to gravitate to the APC 5.7x3 or the 6x2 for modern hi-revving .061 glows. A diesel generally swings a larger prop. A Cox reedie uses from 5x3 to 6x3, depending on porting, etc.

If you have a specific engine in mind, let us know. I'm sure someone has flown it.

George