I'm only training, so nowhere near as experienced as the guys above, but I regularly fly a Warrior from 615M of grass, usually with two and occasionally three largish adults(650lb - total - not each) and full fuel.
Good short field technique and a decent headwind will see the wheels off the ground after perhaps 350M, and then allow the a/c to accelerate in ground effect. The headwind seems to make a huge difference, especially on landings, which do have to be quite accurate. The correct speed over the fence is essential.
We do sometimes use the 550M runway, but only with two people on board for training flights. Club rules state that there must be at least 10kts of headwind for student solos on this r/way, so I guess that underlines the point about the wind.