You can overpower an airplane and upset the design parameters even if you get the CG right. A lot depends on where you fly and what the runway conditions are. I like a .60 in the Senior Kadet but then I fly at 5000' ASL where density altitude and temperature begin to take over. I have always failed to understand why manufacturers list a 78" model like the Senior Kadet as requiring power from a .25 to a .40. At sea level, 2995 " of mercury and 65 deg. F it might work. That's a standard atmosphere and all full scale designers state the useful load, range and gross weight based on that figure. They also supply a graph in the pilot's handbook to compensate for current conditions at your site. With RC models you have to figure it out for yourself. Just remember, on a hot day at high altitude the largest size recommended by the manufacturer plus one size up will do the trick. Putting a 454 V8 in a cigar box will make it go real fast but it's not a good practice.