yeah it is noticeable slower as the 940.I think the stab is a matter of skill and conditions and i,m pretty sure yours are a lot better then mine

On relative flat water I really like the 399 stab (I don't have a 370). It is faster and less drag. In conditions like I had today side-on, 5m on the small side with knee high chop from every possible direction and slow windswell running through it that is actually hard to find a spot to pump you board on the foil without running straight in the next knee or bigger chop I prefer the 483 stab because it offers more grip and control and a lower stall speedIn conditions like today (that are even for here are like sh#t) the 940 simply needs too much speed and goes faster as the swell running through while the higher stall speed makes it difficult to jibe in between that mess.
The Balz offers at least for such conditions often the right speed to ride the swell.
When it is cleaner and we have for here longer lines (7sec period is considered good over here) the 940 and 399 is really good.