Bdtyktl

For a fantasy race or for bio-augmented humans, how durable would they have to be to walk away from a 1000ft free fall unscathed? And how would this logically translate to other forms of durability? Would it make gunfire from calibers like 9mm or .45 entirely ineffectual? What about more powerful rounds like .308 or even .50cal? Would the force from a bullet that powerful be enough to crack the skull of someone able to survive landing on their head if pushed off a skyscraper?

Normal human durability, and a lot of luck

People have survived terminal velocity falls. In 1972, Vesna Vulović fell over 33,330 ft without a parachute after the plane she was in exploded. She didn't exactly walk away from the fall, however. She spent days in a coma, and was hospitalized for months after that. But she did survive.

Vulović is not the only one to survive a fall that should have killed them. They all had varying degrees of injury, so perhaps it's not quite accurate to say that normal human durability is all that's required. But the point is that there are a great many factors involved in surviving a fall, and the height and the body's structure are only two of them.

That said, here are some other suggestions of the types of people who would fall well:

Lighter people

From On Being the Right Size by J. B. S. Haldane:

To the mouse and any smaller animal [gravity] presents practically no dangers. You can drop a mouse down a thousand-yard mine shaft; and, on arriving at the bottom, it gets a slight shock and walks away, provided that the ground is fairly soft. A rat is killed, a man is broken, a horse splashes. For the resistance presented to movement by the air is proportional to the surface of the moving object. Divide an animal’s length, breadth, and height each by ten; its weight is reduced to a thousandth, but its surface only to a hundredth. So the resistance to falling in the case of the small animal is relatively ten times greater than the driving force.

Terminal velocity is a function of (among other things) weight. The lighter you are, the lower the velocity at which you hit the ground, and the easier it is for you to survive.

Wider people

Wingsuit flying is a reasonably popular sport where flyers skydive in a suit with "wings" between the arms and body, and between the legs. These jumps typically end with a parachute, but in 2012, Gary Connery landed a 2,400 ft jump without a parachute, landing on a "runway" of cardboard boxes.

Also, having wings gives you more ability to steer towards softer ground, which is always a plus.

The best enhancements for falling durability are not going to make you bulletproof

Bullets kill by piercing - by applying a large amount of force in a small area, they are able to penetrate the protective layers of our bodies and apply that force to the vulnerable parts of our bodies. That's why bulletproof materials function by preventing the piercing effect and distributing the force over a larger area.

That sort of protection is not going to help against a fall, where the entire area of your body is experiencing the massive forces involved. Conversely, the cushioning and strengthening of the enhancements needed to protect against a fall are not going to do much to stop the piercing effects of a bullet.