Make the amount of bonus movement points from temporary speed directly dependent on its remaining duration, with it gradually decreasing back to normal as the speed wears off. Also provide diminishing returns where giving yourself more speed boosts on top of already having temporary speed gives you less extra duration than it otherwise would, until eventually you can’t get any more duration than 1 per turn. These bonus movement points should also stack directly with all other speed sources, and be visible to the user in the status bar.