For one of my projects I noticed that slow lookups in minimongo were a major factor in making the templates render slowly, so I created a package that adds indices to minimongo. I thought it might be of interest to some others as well, so I published it on atmosphere as helfer:minimongo-index. You can try it out by running
meteor add helfer:minimongo-index in your project directory.
The package is still experimental at this stage, but in our app where we had a collection with 415 elements, we managed to speed up the find() function by a factor of 20, with corresponding effects on the rendering time.
More information is in the readme on the package’s github repo.
If you have large collections on the client and think minimongo might be slowing down your rendering time, give it a try and let me know how it works. If there’s enough interest, I can develop it into a fully fledged indexing package that also speeds up sorting (it doesn’t right now).
PS: If anyone knows of a better way to modify meteor internals other than redefining the functions with your own code, please let me know!