A guy in my training group who is a 2:47 marathoner did one and finished second. He did minimal "Spartan" specific training. Just made sure that he could carry his body weight with his arms for the jungle gym-type obstacles. The big jock guys would usually get across the obstacles a bit quicker, but the really big guys struggle against their body weight. But, every time the course opened up into a run, he would pass people like they were going in the opposite direction. As long as the course is as long as 10-12 miles, any quality local runner would dominate over the gym rat/crossfit types. There is just too much running involved to even out the advantage on strength obstacles.