It's really rough estimation. I said at least. It might actually take more than that.
Edit: 805 was a very huge underestimate. You have better chances at raising your skill by setting a bunch of 760-780 scores than setting one or a few ridiculosly high ones. I just inspected the formula, and it favors a bunch of lower scores over a single high one. To make a comparison, a single 1000 score will put you up as high as having 750 for the first 20.
Edit: 805 was a very huge underestimate. You have better chances at raising your skill by setting a bunch of 760-780 scores than setting one or a few ridiculosly high ones. I just inspected the formula, and it favors a bunch of lower scores over a single high one. To make a comparison, a single 1000 score will put you up as high as having 750 for the first 20.