but you still won't know how fast it will REALLY go until you jump in and fly it.
Or, for the greater of my experience, you don't how slowly it actually goes, until you jump in and fly it!
A retired friend of mine was the lead aerodynamicist for deHavilland Canada. He told me that they had calculated the cruise speeds for the Dash 8-100 to within 2 knots, before it ever flew (and their speeds actually were within the 2 knots). But there was a lot of brain power being applied to that....