A Trailblazer in particular, which can keep up their action boost speed bonus for 18 seconds out of every 20, on top of the extra spring attack distance. This doesn't stack with action boost sprint though, so you lose a bit stacking the two together.
I've found a pure Trailblazer simply outruns a +100% speed horse by keeping at +90% speed most of the time and boosting with spring attack and abundant step.