Here are some rough benchmarks[1]
Performance will vary widely depending on which functions you are calling and characteristics of the data. Some types of analysis will quickly process 500 MB, and others you will probably want to use some sort of indexing strategy.
For pure javascript indexers, check out rbush[2] (R-Tree indexes) and tile-cover[3] (map tile indexes), both of which are as fast or faster than the C++ indexers used in most mainstream spatial databases.
Expect these benchmarks to improve in the coming months as we push the limits with new, faster algorithms as well.
[1] https://gist.github.com/morganherlocker/a9041f2491c63b541cb2