If I keep my 8t drivers they won’t fit on the steel shaft though will they? Because of the different shape of the shafts? So I would have to no matter what but Avid drivers to fit on the steel shaft? I haven’t quite got all the driver and pitch all figured out. If there the same pitch 2.86 a 7t won’t fit A 8t track correct?
Whether 7 tooth or 8 tooth, if your track is 2.86 inch pitch and you want to keep that track, you have to stick with 2.86 pitch. Regardless of tooth count. And regardless of whether you go with hex or splined shaft. If you have a splined style shaft to put back in there with 8 tooth 2.86 pitch drivers, the easiest solution IMHO would be to just put it in there and run it. Realizing it gears you up, but that gets you back on the snow. You can gear it back down using one of the many alternatives; cheapest is to us PRO quickdrive pulleys along with your stock Axys belt. Or you can go with a Kurts gear down, or TKI, or the one from Canada which I forget the name.
Disadvantage of 8 tooth: gears you up (which you can fix - above) and reduces snow evacuation (but no worse than 2011-2015 Pro I believe).
Advantage of 8 tooth (stock style) drivers: lower track rolling resistance (larger diameter), and I am sure there are other advantages I am forgetting. Should not need to trim rails.
Just an FYI, I bought the 7-tooth involute style drivers from Avid and put them on my 2015 Pro QD hex shaft before Polaris even came out with the Axys 7-tooth, so I could gear it down without gearing it down. Using the close-to- stock style meant no trimming rails and no antistab needed. I ended up picking up a Kurts gear-down setup cheap and went back to stock 8T drivers and sold the Avid 7T (and took a bath on that, but hey, that is sledding).
So if you don't want to fool with gearing etc., stay stock 7T 2.86 pitch with either hex or splined drive shaft depending on what you can find for sale... for a little more punch off the line and in the mountains, for the 7 tooth setup, pick up a used set of quickdrive gears off a 2013-15 Pro, which will work with your stock Axys QD belt. I have sold a number of sets of those myself, they go for $130-150 typically, seen some for sale on facebook's "mountain sledder swapmeet", separately or as part of Pro part-out sales...
Hope that helps.