The body does not allow vitamin C pools to expand beyond about 3 grams. Probably because there is a toxic side reaction associated with higher bodily pools. Possibly the double strand breaks in DNA that vitamin C plus copper would catalyze wherever copper is already bound to DNA.
How much more than 3 grams would be toxic? If it is 4 grams, then 3 grams may be way too much. If it is 10-30 grams, 3 grams might be optimal. It all depends when the putative toxic side reaction kicks in.