I saw about a 5 inch one for sale at my LFS one day, and he was missing the next day. I looked at the panther grouper, and he had a tail sticking out of his mouth. The grouper was MAYBE 6 or 7 inches long, and the tail was the last bit of 'cuda that wouldn't fit down the hatch. They can't be that mean if a panther ate him!
When my parents went to the Virgin Islands for their honeymoon my stepdad, who is 6'4", was swimming in the water for at least 10 mintues with a HUGE 'cuda, he said probably at least as long as he is tall, and he just sat there and hovered, never made a move.