Top speed for a 767 is 898 kph/558 mph and that is at an altitude of about 30,000 feet, source: http://www.zap16.com/2009/10/23/boeing-767-200/
at 30,000 feet the atmosphere is 1/3 the thickness of atmosphere at 700 feet. This would cause approximately 3 times as much drag so the top speed would be about 1/3 of the top speed at 30,000 feet, or about 200 to 300 mph at best, and that is with no wind.