Its obvious that its a matter of prefrence and if you are a scale guy you would expect to put an engine in your plane that will make it look and fly authentic. However I see the biggest reason for overpowering is for 3D flying. You need that reserve power for manuvers slow and low that may stall your plane and make it unrecoverable with the reccomended engine. I cannot remember what magazine I read it in but it was on a an Extra 300 or 330 and the article stated that the recomended engine wouldnt be enough for 3D and that the tester pilot used an enormous engine for the plane and specifically noted to use caution when flying because unless you were on an up line you could not go full throttle because it would tear the plane apart. And the maufacture put a disclosure in the instructionds that using an overpowered engine would void the warranty of the ARF. I am currently assembling a Funtana 90 with a YS 1.40 sport. To quote "not more than you need just more than your used to."