Below 1500 is probably always too low for flooring it for any purpose at all. But above that, in a naturally aspirated and relatively low-power engine that is also in good working order, there is not much chance of damage. ECUs will adjust timing and AFR as needed to avoid pre-detonation. Nonetheless, 1500 is my absolute bottom for relatively high load (75%, which is a long way from WOT). But generally I am at 1700 or higher as I accelerate. Been doing this for years all the time and have 248,000 miles on the original engine now.
Great video here: