I've seen those numbers before somewhere and I've never quite understood how to use them...
There are so many things that affect how a plane will fly and is designed to fly. And why would merely the size of the engine be any reliable measure of the power output, maximum thrust might be a better measure?

Perhaps one can used it the other way around instead. Lets say you have a sunday flyer design and want to know what engine size to go for, then you have a rough guide by using 300+ (anything less would be overpowered). If instead you want to impress you mates with a speed design then you should aim for <200