UPDATE:

I posted this in the Voyageur thread, but I'll post it here as well in case anyone comes across this later. This thread has three more 84/85 VSP owners, in addition to Schreck, saying their seatposts are marked 27.2. So, it would seem I do have the wrong size on my bike currently. The carbon grip has been holding, but I think I'll be looking for a 27.2 seatpost now.