I’ve thought of the point where password length becomes irrelevant as well. Unless there some maths I don’t know that plays a role here, longer passwords become useless when x^n > K. Where x is the character set available for the password, n is the smallest length that meets the criteria of the formula, and K is the hash functions key space. Effectively, this would be due to the fact that brute forcing would be just as likely to find a collision as it would the actual password used.