It's difficult to rate a film higher than 8.5. In my opinion, imdb has just about been ruined with inflated scores plus shills, plus trolls severely criticizing and underscoring to possibly get even(say by a disgruntled production worker).
Then, films lose their relevance in time which lowers the score.
Then, who we are when young and scoring a film, can dramatically change the score a decade or two later.
Even with favorite films, I tend to lower the score to a realistic one.
Name a film you'd rate the highest score and why.