Over all the balance of the horse should basically make a square in its shape. If you lovingly cut the horses neck off at the shoulder you can see a box shape. It should be a tall rectangle or square. Not longer than it is tall.
I have a good example of too long below. He is standing at a bit on an angle but if you cut his neck off he is a long rectangle. He is simply too long bodied.
Here is a better balanced horse who is not so long. If we cut his neck off he is a tall rectangle.
The reason we might prefer this confirmation more is not the height, but the balance. The 2nd horse will be able to balance himself because the length of his lever is shorter. IF all things are equal I pick the horse that is short bodied over longer bodied.
Both the top 2 horses give up some in length of neck. The length of neck helps balance the pendulum. I like the length of neck of the 3rd horse compared to the rest of his body.
The 2nd and 3rd horses are both VERY athletic. However, the temperament of the 1st horse is what put him in the Kalsem Paddock. Obviously sometimes temperament is the most important.