Martin,
I've had the same helibar/higher screen/Ventura combination on a 996, but am only 6'3" and had no problems with weaving and that included 160mph.
I did fit new tyres before the trip, so wonder if your slight weave may just be down to part worn tyres if they weren't new, or possibly 2" does make a difference. Ask the ladezz on that last point
