I was messing around on the Protectorate of Plort map, and I decided to test one of the most powerful horses known in minecraft, with a command block. This command was originally devised by a guy named Direranger50 on a LOtR server, in which he was trying to create a steed faster than Edward_Blum's horse, which was appropriately named "Sanic". I have adapted it to work in 1.8, and I dare you to try tame this thing. I believe this thing can be truly named "Shadowfax"; it ran across Plort in less than 20 seconds. Here is the command:
/summon EntityHorse ~0 ~1 ~0 {Attributes:[{Name:generic.maxHealth,Base:1000.000},{Name:generic.movementSpeed,Base:2.0},{Name:horse.jumpStrength,Base:99.0}],Type:0,Tame:1,SaddleItem:{id:329}}

Note: Even with a movement speed of 2, this horse will still run at absurd speeds, i.e., faster than my framerate. This horse must be spawned in tame, or else it will be impossible to catch, much less ride.

What do you think?