There is a potential performance win to change the data tables (as opposed to the index or metadata/catalog tables) to use column store format instead of row store (see: http://source.wiredtiger.com/develop/schema.html#schema_format_types).

This is because each document is stored with an internal integer id and normal access patterns can take advantage of columnar lookup. This would require a great deal of testing to prove out, but we've seen up to 30% perf improvements with some read only workloads.