Anyone would think that Take-Off Performance is an exact science; which at best is an averaged set of numbers that will give some guidance as to where you 'might' actually stop if it all goes pear-shaped.
Hey, three to five knots is probably a good range that an 'averaged fleet' might achieve; within a couple of hundred yards of that vital bit of runway that allegedly guarantees you stopping within the remaining 'stopway'... hence, eating dirt! Given that you and I have the same aeroplane, both of them will differ by an incalculable amount; therefore, does it really matter? During my Performance Course, many many years ago, I recall that a couple of seconds or so were factored into the numbers to allow for pilot recognition/response time of an engine failure... why beat yourself around the head with trying to get the words out in time when the response time has allready been factored-in? So what, if you're a couple of milli-seconds overdue in making the call; don't anticipate it... just do it! There will, in all probability, be a difference of a couple of knots between the ASIs anyway! Perfectionism is one thing... but let's not take it too far!
TCF