That's all fine, and indeed a good idea for ab-inition students to have something to give them a reference.
But, and here is a good but, what exactly are these figures based on?
Take a brand new engine in a clean airframe with minimal kit and they probably hold good. But what about a filtyhy airframe (we've all seen them) that can cost a couple of knots, and what if the engine is getting tired, what about if the owners have installed every conceivable toy in the instrument panel. The whole thing could weight 100/200 kilos more, or worse than that.
As with cars, the manufacturer might say it can do 150 mph, but that is the book speed, in perfect conditions, with a highly trained driver, on a test track. The reality is take 2 C class mercs from about 1998 (like mine). Mine is in the garage for regular service, isn't thrashed, any little thing that goes wrong is fixed, I am sure it will do the book speed, or damn close to it. Compare that to one that hasn't been near a service centre for 3 years, has infrequent oil changes and so-on. I will pay money to see someone try and get the book speed out of it.
What I am trying to say, is that although there might be a standard set of figures, each individual aircraft is different, only by a couple of knots here and there, but that can be critical in some circumstances, best to fly to a standard set of numbers that exceed what the book says by a few knots, for the wife and kids if you like.