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A marinating steak should be cooked low and slow, because it is often a tougher cut of meat and that helps it become more tender. Note: This does not mean they should be overcooked!
A grilling steak generally should be cooked at a higher heat. You can sear each side for 60-90 seconds then a few mins on each side depending on how thick the cut is. I use a pressure test to determine if to is done, using the firmness of the ball of your hand in different positions.
edit: Found the "Finger Test" for steaks
http://simplyrecipes.com/recipes/the...eness_of_meat/