I’m actually not too sure how right you are here, my last cat was a chunky boy at 7kg, let’s say that the upper end 68mg is the LD50, I’m roughly 70kg, 680mg of coffee would be very uncomfortable and unpleasant, but I don’t think I’d be hitting the LD50.

LD50 in humans is probably around 100mg/kg, fatal doses are 150-200mg/kg