Old records claiming 10m or more have long since been discredited, bet here's an Interesting study. Ellis and McCosker, for their 1991 book Great White Shark, checked all the records of huge GWS and concluded the probable total length (TL) of the very largest was around 6.5m (just over 21 feet). I went with this conclusion in my book Shadows of Existence.
Mollet et. al. in 1996 went back and looked at the information, including how various measurements and estimates were done, and concluded the famous Malta shark from 1987 might actually have touched the 7m mark and the shark caught in the same year from Kangaroo Island, South Australia, could have been, and probably was, slightly over 7m. (The Malta shark was measured while lying on a floor: the Aussie shark was estimated against a boat and body parts kept, but it was too big for the fisherman to get it aboard.) So maybe the people who suggested South Africa's fabled Submarine could be 7m long are not far off. I'd be interested to hear what other experts have to say.
("A review of Length Validation Methods and Protocols to Measure Large White Sharks," in 1996 book Great White Sharks: The Biology of Carcharadon carcharias, Academic Press, NY.)
UPDATE: A FaceBook correcpondent, Caludio Dino Galetovic, sent a 1998 article saying the Malta shark might have been measured over the curves rather than in a direct line head-to-tail. This would make it under 6m. Well, darn.
The Great White isn't the human-hating monster of legend, but no one would deny it's formidable