Originally Posted by draftrider
It would depend on the horse and its build. All horses of one breed are not built the same. Look for a perch with a more sloping shoulder versus an upright shoulder, and one that can track his back legs well under him.
Not something you can make a blanket statement on.
Draft horses (generalization) are designed to pull with their strong front ends. Their back ends are not designed to push underneath like you want in a dressage horse.
It also depends on what level of dressage you are aiming to do. Any horse can do lower levels.