I fed mine bloodworms when very little, and feeders(you say they're hard to get...) I'd go with krill, if it will accept it, or small pieces of chicken. Mine at 12-13" is eating well on Hikari Massivore Delite. Earthworms go down well. I've never had terrible aggression problems yet, but he had tank mates from the beginning.
As stated, all individual's have their own temperament, but I most commonly hear them getting bad at the 8-10" mark. Again, mine hasn't gone ape yet, but it could come any day. He did eat some 4-5" Scombs (sabertooth tetra's) he must have really liked them, since he ate 3, doh!
I love the ARTC tho, and I couldn't go without.