Check Again on IAS for B757
It might be worthwhile checking a little more carefully on the information concerning the B757 bird impact speeds. According to the information I have, the speed used for FAR 25 certification is Vc and is reduced linearly to 0.85of Vc at 8,000 feet to achieve a constant TAS for the impact force equation. This would make a 313 IAS at 8000 feet somehwere around 368 IAS at Sea level. This would exceed Vd and or Vmo and by definition Vc will be less than these two speeds.
Further to this the bird weight used for certification is 4 lbs for the windshield and structure and 8 lbs for the empennage. The final certification criteria to consider is that it only considers a single bird. Given that the higher you go the likelihood is you will encounter flocking migratory birds i.e. waterfowl and that the populations are skyrocketing and their average weight is increasing (based on survey data), you might want to think twice about high speed low altitude operations. In the last twelve months there have been a number of serious strikes with geese at speeds below certification speeds that led to windshield penetrations, structural damage and flight crew injury.
As far as engines go, other than the ultra-large engines used on B777 jet engines are only certified to take a single 4 lb bird at the aircraft liftoff speed. Even then they are only required to not catch fire, suffer an uncontained failure, lose the capability of being shutdown, suffer no more than a 25% thrust loss and keep running for 5 minutes.
As for Houston... In 1998 a B727 struck a flock of snow geese (~6.5 lbs) at night at 280 knots IAS. The results were nearly catastrophic - damage to all three engines, leading edge devices, airspeed system. Fortunately there was a Flight Engineer check airman on board to assist with the mutliple failures and the ear-splitting cockpit noise from the damaged radome.
As for the efficiencies to be gained, that is another story that requires careful analysis from a "total system" perspective i.e. if you have an efficient speed of 290 ias for a particular aircraft on day-of-flight, but you are asked to fly at 320 ias. The net result will be an incremental loss in efficiency. A highly complex analysis to say the least.
Approach high speed low altitude operations with great care it might be fatal.