May as well draw a hard line and never put larger than a 31" tire on any Jeep you build. It is about the same difference in performance when you need something to work better. If I had to give up all of my M12 Fuel stuff, I'd snivel a bunch about a couple of items, but I'd do it in a heartbeat. You simply can not beat their Fuel grinders, Sawzall, larger impacts, and drills. Once you use the Fuel drill in M18, the little M12 will rarely get used again. You can push harder, spin a bit faster, and drill much larger holes when you need to. If I saw any of my helpers ever chuck up a 2" hole saw in the M12 for anything but plastic, I'd likely slam it on the ground to render it useless so they would never do that shit again.
M18 is the way for weed trimmers and leaf blowers too.