Going to a store and trying on a lot of shoes is the best way to figure that out. That aside, if you want to know what that differential is, it is normally listed on shoes, especially on running-specific websites. For example: https://www.runningwarehouse.com/Brooks_Ghost_12/descpage-BGH12MB.html

Notice the stack height details. The Brooks Ghost has a 12mm differential. 8-14mm is probably a good place to start. As others have said, avoid hill sprints for a bit.