According to this article by REI, it's your torso length that determines best fit, not your height. I was shocked to discover that mine is only 19" even though I'm 5'8" tall. Maybe that's why my Convertible Carry-On was never comfortable on me.
After being inspired by Jane from Sapulpa, I'm going to get the Appenzell and do my best to pack lighter than I already do. I usually travel for 4+ weeks but pack for 1 week. I've been using carry-on wheeled bags for the past few trips. I'm hoping to switch back to the backpack to have my hands free.
Weight on your back is also a factor, but it's still an issue with a wheeled bag because you have to manage your luggage yourself. BTW, I'm 72.