The best way to judge the "doneness" of a steak-- of any kind-- is a simple touch test. With your right index finger, press the soft fleshy bit at the base of your thumb, keeping your thumb relaxed. The muscle should feel soft and squishy. That's the feel of rare meat. Now pull your thumb toward your palm and notice how the muscle becomes firmer and firmer. So does steak when you cook it. So a relaxed feel equates to a rare steak, a semifirm feeling to a medium steak, and a firm feel to a well-done steak. Practice this a few times and you'll be able to judge how well a piece of steak is cooked by feel alone. This is much more reliable than timings because every steak is different and cooks at a different speed.