I just got off the phone with TRAXXAS, and YES, they do have different settings on each Maxx they make. The grub screw is installed by the computerized robots and there is no magic number. The 6.5 might have come from someone dismantling it on their own and figuring it out.
When asked what a good starting point is, the tech said with the tranny open and the gear set in hand put the shift set screw so that the top of the grub screw is just flush with the top threads of its threaded recess. From there use 1/8 turns in or out until the tranny shifts as it should. He also recommended using a spot of medium loctite on the set screw to minimize any vibration caused backing out of the set screw. From there, I refer you back to my original post for obtaining the procedure for making the adjustments.