I know what you are thinking, and I haven't done any research, but have seen a few 80s GM X bodies around here get in major accidents at 15-30 mph impacts, and still be driveable. They seem to be built better than any other small compact car of the 80s for head-ons and rearends. Case in point, a lady near my house was hit in her 80 Skylark in the front by someone going 55. Actually, it was not a head-on, but a t swipe where she got spinned around. The car is still driveable minus the missing headlight and popped fender. The hood is still straight. Another Skylark crashed into a Ford LTD, and the Ford was totalled. The rear bumper of the Buick was bent down at a 45 degree angle, but the car was still driveable and is still being driven. An 80s Olds Omega was rearended at 35 mph, and the bumper is crooked and the frame a little bent, but the car is still driveable. Also, these people driving these X bodies seem to have the attitude that they drive a little econotank. The lady with the 80 Skylark said it was the best car she ever owned. I have a soft spot for X bodies.
Sorry folks, but I really don't think our Ks would hold up well in anything more than a 5-10mph impact.