Definately rare to med rare. A marinade that we did at work that was really killer with hanger steaks, should work great with flanks as well, was amber bock, soy, brown sugar, garlic, rosemery, dijon mustard, and some EVOO. Grilled em up, rested/ sliced, and served them with buttermilk onion straws and a maytag blue cheese, bacon, horse radish sauce.