Its probably also all over the board, but in one dose, the consensus is 1000mg.
Admittedly I frequently take 2500mg all at once and the worst that happens is I yak in a couple hours or I yak when I wake up the next day.
I believe taking more than 1000mg at once is too much for your liver to metabolize and this is where problems arise. Your liver won't give out (probably) if you go over 1000 but under 4000mg, but Id bet money that the cumulative effects of this, long term, will lead to liver damage.
I suck at doing CWE so I usually just suck it up and take my 2500mg but I know I need to stop and find a better solution.