Hi again Luc.
Actually, if you leave a vessel at rest, unachored, the wind does cause it to drift off station. Now, that may be the wave effect rather than the wind, but it does happen. It can take a while to see it, though.
I am testing this by producing a simple mission (1 way point) and changing the environment. I don't know if makes a difference. (You may be doing it differently).
Anyhow, all this is getting away from "Does the Rank affect the top speed?". If we accept what was said originally, that all variables are identical except rank, then it must be rank. Is there an easy way to change that and see if it has the claimed effect?