If the WTC towers were built to withstand multple hits from a 707?

as told by the engineering firm Worthinton, Skilling, Helle and Jackson who were responsible for the structural design of the twin towers, and the kenitic energy released from a Boeing 707 at cruising speed is 4.136 billion ft lbs of force and the kinetic energy released by a Boeing 767 is 3.706 billion ft lbs of force, due to the fact a 707's crusing speed is 600 mph and the 2 767's were reported by NIST as travelling at 440 and 540 mph respectivley, it appears that a 707 would cause more structural damage, if this is the case how can NIST stick to the theory that the mive damage to the twin towers was caused by the aircrafts m, high speed and momentum causing the towers to collapse?