I don't think anyone will really know until B6.1D cars hit a wet astro track but I am fairly confident they will be THE hot ticket with the layback gearbox.
Recently I've spent many cold & wet hours at Kidderminster with grip levels less than that of ice on the areas in front of the rostrum and against laptiming the laydown is definitely quicker and realative consistency is the same for both.
Only thing I'm doing is trying to get the weight as far back as possible without adding additional weight to the car. Based on this being able to move both the motor and battery back 8-10mm (estimated from images) will be a huge benefit.
Now I've typed that watch us have the driest and warmest season on record