Vilas, I'm not saying you are wrong, but that is a sweeping statement.
I'm sure Rat5 is looking for hard evidence to back all that up, and I'm not so sure either, and between us we've probably got 50 years experience. Plus the manufacturer, FCTM and the performance gurus all have slopey shoulders on the subject.
As it goes we use steady wind for perf calculations at our place, at the planning stage at least.