What is Nidalee's Javelin Toss damage cap?

Nidalee's Javelin Toss is an ability that deals increased damage the further you are from the enemy it hits at the time of contact. This ability is stated to deal 250% damage at maximum range, but sometimes it appears to be more than that.

Is the 250% multiplier a hard cap, such that no added distance no longer helps after that point?

If 250% isn't a hard cap, what would be Nidalee's maximum damage at level 1, assuming ally help. (i.e. Thresh lantern recall)