In a straight up fight Khan should win. Look at how Spock did against a Khan that had been injured by a spaceship crash. Khan just has better feats. Vulcan's are strong, but Khan was kicking dudes hard enough they flew like 20 feet away. I think the Vulcan's best feats are holding up a person easily by their neck one handed.
Someone else had to beam done and shoot Khan a bunch of times in order for Spock not be dead.