Granted the "turbo" cranks with their rolled fillet journals add a measure of strength to the big picture, I've heard of NA cranks going real fast....it's all about keeping the detonation to a MINIMUM and not spinning it to the moon and back. For what it's worth, I know of a .020/.020 under turbo crank that was spun to 6100 rpm on every shift and didn't break even when 4 of the 6 pistons were vented.
