From reprint of The Peregrine, J. A. Baker’s classic of British nature writing:
The peregrine swoops down towards his prey. As he descends, his legs are extended forward till the feet are underneath his breast. The toes are clenched, with the long hind toe projecting below the three front ones, which are bent up out of the way. He passes close to the bird, almost touching it with his body, and still moving very fast. His extended hind toe (or toes — sometimes one, sometimes both) gashes into the back or breast of the bird, like a knife. At the moment of impact the hawk raises his wings above his back. If the prey is cleanly hit — and it is usually hit hard or missed altogether — it dies at once, either from shock or from the perforation of some vital organ. A peregrine weights between 1 1/2 and 2 1/2 lbs.; such a weight, falling from a hundred feet, will kill all but the largest birds.
If a peregrine weighs 2 pounds and is going 90 miles an hour in a stoop (they can go much faster), that's the equivalent of a 14,000 grain ball going at 132 feet per second, so the impact would be 541 foot/pounds of energy.
For comparison, a handgun firing a .22 long is about 120, a handgun firing a 9 mm is about 385 and a handgun firing a .45 is about 420 at the muzzle.