AFAIK Boeing SOP is to perform the Engine Fire (...) NNC and only evacuate if you can't extinguish the fire.
Operators with more common sense use the "Airbus" approach, that is perfectly applicable to 737 - discharge both bottles and commence evacuation immediately.
I disagree with the confirmation of engine fire switches on ground. You are loosing precious time that could be used to start evacuation. Even if you discharge the bottles in to the wrong engine - for which you would have to ignore the large red engine fire switch and use that annoying override button that is much more stiff on the real aircraft than in the sim (hint: frequency of use) - the worst case scenario is that you can't extinguish the fire, but you'll be far away from the aircraft by the time it becomes an issue.