Quote Originally Posted by Spino
This is actually a popular misconception about the mounts used by most knights, especially for the period we're discussing.

It turns out that most knights actually preferred the moderate sized breeds, especially those from areas like Spain. The main reason being that those breeds were faster and could change direction quite rapidly in less time and over a much shorter distance. Draft horses may be larger and more powerful but they require too much management and planning on the part of the rider to maneuver properly in combat. Larger draft horses are also less comfortable to ride with their wider frame and heavier impact on the ground. The ill effects on a rider's spine are more pronounced with the larger breeds. Late era knights only rode these large, specialized breeds in combat and used a normal sized horse for all other functions. A moderate sized horse can handle the weight of a heavily armored rider just fine so long as it is not overworked in combat (i.e. run all over creation like light horse would when engaged in skirmishing and harrassment activity).

One thing for sure is that use of the larger, draft breeds was probably more widespread in the 'Late Era' when large amounts of lamellar, chain and especially plate armor were used to protect the horse.

On an aside I know some knights also preferred certain Spanish breeds because of the added bonus of them giving the appearance of being proud and confident thanks to unusually high position and movement of their head when walking or galloping. At first glance it seems as if the rider is forcing the horse to rear its head back but it's a peculiarity of the breed.

Considering that the Spanish Bred of horses can be seen all over the Western United States as wild horses - durable, fast, medium sized at appoximately 13 hands on average. You might be correct.