Apologies for taking time to reply, computer problems
Shawn, some of the performance figures can be checked on a regular basis, ie. single engine rate of climb (CAA air test), engine performance figures, but some are a bit more "intangible"
For example, rejected take off distance, these involve pilot performance as well as aircraft performance. When I flew in the US, various pilots who were far more experienced than me repeatedly told me - the flight manual figures are the very best you can expect, always add your own safety factor depending on individual circumstances. I have always flown with that in mind, so far without mishap
But am I adding safety factor on top of safety factor?