Among flying birds, some of the strongest wings (structurally speaking) belong to peregrine falcons (that measurement comes from my own work).
Here's why: http://www.airspacemag.com/flight-today/falcon.html
Frightful, the world record holder, exceeds 242 mph in a stoop, and can pull out of such dives carrying a lure equal in mass to herself. The best comparison I can think of is this: drop down the middle of a spiral stairwell, and catch yourself on the railings at the bottom with your arms. With a compact car attached to your back.