Matt,
Height to weight ratio probably isn't the best comparison, since you don't know where the weight is distributed from tractor to tractor. Obviously,wider is better. But if the Kioti has it's extra weight below the center of gravity, it might actually be more stable even if it is narrower. Not saying it is; don't know for sure; and that is the point.
I own a Kioti and from what I can tell the weight is the the axles and transfer case. The engine sits low, very low too. Though, from what I've seen, most of the machines in the class all have similar engine mountings.
I've used CK25 on some pretty steep slopes. In fact, that is one of the reasons I liked it: heavy down low and wider than most I looked at. I most work mine on such slopes, and with loaded tires it's quite the beast, allowing me to work with heavy FEL loads without much concern for rollover or tipping.
From what I can tell, the MF seems like a really nice tractor. And if you can get into one with similar features for the same money, I'd probably go that way over the Kioti. But, I don't believe there is any appreciable difference in stability between them. Of course wider is wider, and certainly helps a great deal.
Also, remember that wider means that all your implements might have to be wider as well in order to cover your wheelbase. Wider implements might adversely affect your stability too, and make it harder to maneuver in tight spaces.