In the SCCA ITS racing world it was somewhat common to hold full throttle between 7,000 and 7,300 rpm for 5 or 6 seconds at a time on each lap due to the transmission limitations in the SCCA rule book. That's with cast pistons and a stock damper. Cranks do break from that use especially if the damper is old - I've seen it and I've seen a damper pop off the front of the crank, go through the hood of a car, and into the windshield of the third car in the line racing for turn 1. That's where a lot of these crank harmonic rumors came from. There are also the fools who used to remove the damper completely and replace it with an aluminum under drive pulley set. Still very common in the BMW world and you see posts weekly on Bimmer Forums from people wondering why their crank snapped between 3 and 4.