I would think you could make "them" go faster, just by upping the horsepower, etc., in the aircraft.cfg. The whole formation is just one 'aircraft' in the eyes of FSX, flying by the single standard aircraft.cfg and .air file, and so should be as modifiable as any other single aircraft in FSX. If I remember correctly, I think I made the formation fly at approx. 150 mph IAS (which is a True Airspeed of approx. 240 mph at the formation altitude of 27,000 ft), which falls between the to-target and from-target airspeeds the formations used to follow (155 mph going to target, 140 mph on the way back).
There should be nothing stopping modifying the formation's airspeed. Have you tried AirWrench?
Mike