Fact:
The recorded fastest horse breeds include the Thoroughbred racehorse, which can run at up to 44 miles per hour (70.8 kilometers per hour), and the American Quarter Horse.
Some of the best sprinters can run up to 55 MPH (88.5 KPH.)
Naturally. This only counts for standard horse breeds that humans have access to today. They pale in comparison to those of much more luxurious and supernatural standards, such as pegasi.