Hi Mogambo! Your step height should be determined by being able to stay in your training zone, not by your body height.
You should use the step height that keeps you in your training zone. Most people can do that on 6 inches. If you find that 6 inches is not challenging enough, then go to an 8 inch height. If at 8 inches you still do not feel challenged, then increase your arm intensity or use more propulsion RATHER THAN increasing your step height to 10 inches. Studies have proven that the rate of injuries increases dramatically when the step height is increased to 10 inches. Happy Stepping!