All this is all very well especially if you are renting aeroplanes but to a lot their aircraft is their own pride and joy.
Do you accept the book stall speeds or do you get the actual figures as well as behaviour on your own aircraft?
Two identical aircraft can be very different one stalls straight ahead wings level the other drops a wing etc.
If you know every burp your aircraft makes you will know how short a grass strip you can get in and out of how she handles wet grass, soft ground etc.
A PA28 30 years old with hangar rash, bad paint, a few bumps and bulges, a scattering of bugs over the wings and a knackered old smokey aint going to approach the book figures.
Know your individual aircraft and even work out your own actual figures.
In the case of new aircraft a lot is marketing. We know only too well the pre release figures claimed on the Diamond Twin Star 210 kts at 12000 feet on 135 hp???
Pace