In general, Welsh ponies have an average walking speed of 4-5 miles per hour, a trotting speed of 7-8 miles per hour, and a cantering speed of 10-12 miles per hour. However, it's unlikely that a Welsh pony with a rider would maintain maximum speeds for a prolonged period due to endurance limitations.
For reference, the maximum speed recorded for a Thoroughbred racehorse was approximately 43.97 miles per hour (70.76 kilometers per hour) achieved by Winning Brew during a race in 2008. This demonstrates the significant differences in speed capabilities between racing breeds and ponies like Welsh ponies.