Best format for high-performance Serde?

I'm currently working on a small game in rust and I want to be able to serialize/deserialize save-games efficiently. I'm currently using RON for both the savegames and the config files and it's working correctly but saving is a bit slow. What are good formats for fast serialization?

Note: It doesn't need to be human-readable, I've just been using RON so far because it was easy for debugging. In fact, I'd prefer a format that can't be as easily manipulated by a human just using a text editor.