The free tropical horse and wolf from summer's Tropical Atoll or the Item Shop horse can't be quicker in any other way than with a Kelpie mount - it takes the form of any mount but moves as fast as your fastest mount with a special Item Shop treat. Minimum speed of the Kelpie is 13 yard without the treat.
The Item Shop horse is already the updated faster horse Noble Steed with speed of 9.10 yards at level 6. You can no longer even get the original Kanian Runner that was even slower in its time.
Unless you have seen people ride with quest Courier - that horse runs approx. 13 yards/s but lasts only for an hour or two.
Kelpie mount
Noble Steed mount
PS. I assume the mount is either a horse or a wolf since no other mount is that slow anymore...