I don’t think there exists one implementation that is “the fastest”. Its all about your use case. For example: is your map going to add/remove items during runtime or you do init once and then frequent lookups? This alone would point to completely different implementations.
The fastest server hash is to use AES rounds, pretty much period. The only question is how many rounds and how to seed, and it depends on your scenario. If the filenames are controlled by an adversary, it has to be stronger. If they're not, then it's ~16bytes/cycle.