There is no such thing as a maximum dosage when you start talking about tolerances. There are reliable case studies in medical textbooks of people who have regularly taken more than 1 gram of morphine daily. So, depending on your tolerance, you could take huge amounts of hydro that would be life-threatening to an opiate-naive individual (of course, if what you're using has apap in it, then that's something to watch out for). Codeine is a different story, as it for some reason seems to max out (I think it's 400-500 mg, which would give you a huge histamine reaction anyway), Demerol (I don't remember the numbers, but the limiting factor are the seizures that come with a high dose), Darvocet (toxicity without realizing it), and a few others that I can't recall.

-yawkaw