I have a Kentucky Mountain mare, a palomino, she is very laid back, another one of those that just walks along and has all day to get to her destination regardless of what other horse is around. If you want to open her up she will go, but if you don't want it she's happy with that. Same way with my Rocky mare. She is a bit jiggy at the start but once you let her know speed is not what you want she slows right into a walk and doesn't care where she is in the line up. Every horse has their own temperament and often if you get a horse from the heart of Rocky/KMH land you will have a horse that has a go attitude. It's how they ride there and that's how they break them. You want to slow them down all you need to do is retrain them.
Too bad for the dishonest seller with the fruitcake horse. That's the type you NEVER consider for a broodmare. Every breed is going to get a fruitcake once in a while, no matter how well you keep track of your breeding operation. All you have to do is look at people. Sometimes the wires just don't cross right.
As far as head size, they come in all ranges, most of them are average horse, now the little KMH mare which has a ton of TWH in her far background is pretty petite and usually needs an Arab halter.
Face shapes in mountain horses range from Roman nose to Arab ears and straight faced with very refined bones. Large stocky horses and very fine boned horses, so I can't say that all Rockies are cut from just a few horses, too many different body styles to say they are breeding for all one color. Look around, nowadays you see a lot of champagnes, palominos, sorrels, blacks, bays, buckskins and grullo colors. Yes chocolate is the signature color, but it's not the only color they breed for anymore.
A woman can NEVER have too many horses.....