There are no limits when it comes to hard sci-fi. The following movies are proof of the essence of the genre, which allows us to see the inexplicable.
We took a trip through decades of the genre and came up with a list of the most important and best hard science fiction movies of all time. They are the essence and the foundations of the book of sci-fi rules that's still being written as we, the audience, become much more self-aware of our relationship with technology, the future, and whatever those two will bring.
No Europa Report, probably the hardest of sci-fi movies ever (~9.5 on Mohs scale)? Most movies on that list are somewhere around 5...6 on the Mohs scale, with some (GATTACA, 2001, Ex Machina) around 7...8 and only Martian at 9. Sunshine, Stalker and Coherence are not hard scifi at all, ~2...3.
Well I didn't know that when reading your post, so I googled it and figured that out, but then I found this and believed that there were lists somewhere, so I asked.
So if there is no list of sf hardness, maybe we should write one 😉