No, the size of the 707 was determined by the limitations of having the most powerful engine available in the 1950's. The requirement is that a plane must be able to take off if it loses an engine during takeoff. A 707 having four engines does not have to divert if it has one engine shut down during a flight. That is the major reason why QANTAS still preferrs to fly 747's rather than switch to 777's. If an engine is shut down during flight, they can still continue on to their original destination. A twin engined plane operating under ETOPS rules must divert to the nearest suitable airport if one engine is shut down. Currently 777's must use flight paths which are no more than 180 minutes away from a diversion airport at any time during a flight. Aircraft with three or more engines have no limit to their diversion times with one engine out. Boeing is petitioning the FAA and JAA to extend ETOPS times out to 330 minutes which is 5.5 hours from a diversion airport. This extention if approved, would allow twin engined aircraft to fly almost any route in the world except across Antarctia.
Map showing ETOPS 180 limits.
Map showing ETOPS 330 limits.