I have not cracked one, but the highest HP I've put through one at the track was around 620 hp.
It was/is a 14:1 stock stroke 440 that ran 10.40s at 128-129 mph at 3700 lbs. Ran it for a lil over 3 years and never hurt it.
That same motor is in another car but is making around 700 hp now. It is probably a time bomb, but I'll run it til it dies...if I ever get the rest of the car track worthy.

I know Mike Daurity split the main webs and a couple cylinder walls in his low deck 512/400 stroker in his street car '69 super bee a few years ago. It's around 600 hp on motor plus a small plate system.