750 mph is pretty fast
Its 1100 feet per second in fact.
3,600 and 3,700 ft per second
Which is about 2,500 miles per hour or a tad over Mach 3 as it gets near the ground...
I don't see that as impossible for a streamlined and spin stabilised vehicle with 12,000 pounds of gravitational "thrust" but it would have to be dropped from a height that would exceed the ability of any optical bombsight to aim it. So, its the age old engineering problem of optimising the design - in this case, impact speed and impact resistance versus accuracy, that ends with an optimum dropping height of 18,000 feet and an impact velocity of 1,100 feet per second to achieve the desired penetration of, lets say, a submarine pen.