The X needs two hands as well and I think that could be a problem. You might as well go for the Max if you can't use either one handed. They may have to shrink the XI a bit to appeal to those that want the smaller one handed device. That being said, I think in a week or so I'll be able to use one hand better on the Max than on my old X. For one its not as slippery IMO, and for another it seems easier to use reachability on. I do have large hands but not abnormally so.
my hands aren't huge but I can fully use my X and now XS one handed. some of the rarer reaches to the far upper corner is a slight stretch but I still do it one handed without fear of dropping the phone. Without question I would need two hands to fully use a MAX.