Since the first generation Ventus is a ship truly in
need of a pilot's hand on the stick...then even puttng
2X4's on the ends of the wings probably would help.

A couple of comments on this, you should have better
handling with winglets...so comparing them to non-winglet
wingspan is not really meaningful IMHO. I have flown
side by side with both ships flying winglets and the
two different spans. Your crossover sounds about right....80-90
knots is a typical interthermal speed and that is somewhat
of a coin flip.

However the short wings can carry a lot more water...hence
a lot more wingloading...and when this is the case...the
16.6 gets left behind on the glides.