sorry for the delay in this reply.
The performance figures in the flight manual are based on not requiring favorable conditions, or exceptional pilot alertness or skill.
For takeoff and landing stuff, there is testing done to ensure that 5 knots faster or slower, or maybe 10 feet higher or lower don't have negative effects. And they are tested by other than the factory pilots.
They certainly do not include the use of any transients in limitations of the engine or transmission.
So you may be adding a safety factor on top of a safety factor- but is that a bad thing?