Magneto vs Shield
1. Magneto decides to take SHIELD down, he doesn't have to kill everybody in it, just destroy the organization's functionality. He gets a week of prep. Can he do it?
2. Shield sets up a manhunt for the most dangerous mutant on the planet and Magneto, aware that he is being hunted, decides he'll sink that helicarrier and the bureaucrats behind it in the bottom of the ocean before any damn dirty ape gets his paws on him. Both sides get a month of prep before they make their moves.