16-20 inches work well on the 10-10 saws. Up to 28 inches will fit but it won't have the 'nads to pull it well. Back when my 10-10S (57ccs) was my only saw, I ran a 28 inch on it when I needed to. It did OK as long as I didn't push it and kept the chisel chain sharp. Since yellow fever struck, I run 18 or 20 inchers on the 10-10's and have the 28 incher on my Pro Mac 800. As far as your next saw, if you want to stay in the 10 series the Pro Mac 700 and the 7-10 are good 70cc saws, the Pro Mac 800 and 850 are awesome 80cc saws. For the older Mac's, as Warped suggested the 250 is relatively common, as is the 200 and 300. Parts for these saws are not terribly hard to come by. hth, Jim