Stella is just about 16 hh (maybe 16.1). A whole hand taller than Gia. But she doesn't really feel that much bigger when I ride her. It got me thinking... maybe it's something about the way I'm built, but I've ridden all sizes of horses and seem to fit them all about the same way. (For the record, I'm not terribly tall, 5'3". I don't know what I weigh anymore but more than I want to... plus I'm busty for my size...)
Me on 14hh (Moira)
Me on 15hh (Gia)
Me on 16hh (Stella)
And me on 17hh (Sam)
Now, I realize that I tend to gravitate toward a certain type of horse - more of the Arab and TB type. That may be why the height doesn't feel different, if the body type is the same no matter what the height.
Anyway, like I said, just a random observation :)