By no measure would I say that. I know people in real life who can't go above around 400mg, they only get an increase in histamine response not opioid highness.
My educated opinion is that it comes down to CYP2D6. People like me, who can get a hell of a lot out of codeine, quite like it and take it up to what sounds like crazy doses, probably can metabolize it a lot better then most people can. Just like how around 10% of the Caucasian population are poor CYP2D6 metabolizers and will get little out of drugs that need to be broken down by CYP2D6 to take effect.
Also, holy shit are Mahavishnu Orchestra amazing or what.
ETA:
I would also like to expand on the part here about the histamine response. It can be very dangerous, hence why the LD50 for codeine can seem low to recreational users. It's the histamine response that is dangerous. At the height of my usage, if I took a break for just a few days then dosed at where my tolerance was at, the histamine response would be very powerful. After a use or two though, I develop a tolerance to the histamine response though and it goes away.
Also, expanding on my previous point on The Mahavishnu Orchestra, check out Birds of Fire, specifically the track 'One Word'. Fucking amazing.