The pilot flew the GPS approach and stated he was able to see the runway upon reaching the missed approach point; however, he was not “in a position” to land the airplane. He stated he decided to circle to land with full flaps while maintaining an airspeed of 140 miles per hour. The airplane entered an “unusually high” sink rate during the turn. The pilot added full power and leveled the wings, but the airplane continued to descend. The airplane impacted the terrain off the end of and to the right of the runway. The airplane received substantial damage to the left wing spar. The pilot reported that there were no mechanical failures/malfunctions which resulted in the accident.