Nix does have binary caching (but only if you use `/nix/store` for the nix store path), I'm using it all the time on linux. OSX support is definitly much less s

Nix does have binary caching (but only if you use `/nix/store` for the nix store path), I'm using it all the time on linux. OSX support is definitly much less stable though and there have been problems with build machines for OSX in the past, so I do not know how the situation on OSX regarding binary caches is currently. Regarding your point about build time, I'm not sure why installing with nix would make that much of a difference. Nix still just executes the build system of the underlying packages. However, nix might have to build more packages since it doesn't rely on the underlying system to provide dependencies which helps to make it more robust. Additionally, emacs has various build configurations, which might also require different dependencies, affecting build time.