To actually answer your question, I'm not sure if they're physically stronger but they can take more punishment in Multiplayer. So I guess they kinda are?
Put it this way. Elites are natural born warriors. Spartans aren't too much. Besides this fact, they both under go training at about the same time in life, and come out seasoned veterans. The differences are, most spartans are made spartans because they are born, physically enhanced, and they are genetically messed with. They are also given the high powered armor they have. Elites don't under go all those programs, and only train, and they are muscular. Plus, their gravity is three times earth's, so they are a lot heavier. They have more of a strain on them.
So to answer your question, an elite would destroy a spartan, if said spartan didn't have all of the armor, and perks, and advancements. But in the case they do, it would be about even, though, elites are still slightly bigger, and physically stronger.