The question, as posed, is a little misleading - it seems to be comparing apples to oranges to pears. The question is in fact about the speed of doing fulltext

The question, as posed, is a little misleading - it seems to be comparing apples to oranges to pears. The question is in fact about the speed of doing fulltext search; given a collection of documents in MongoDB, what's the fastest way to perform a fulltext search on them? My solution to this problem has been to use Xapian integrated with my Rails project via MongoMapper and Xapit. It works quite well with the MongoMapper record callbacks (indexes updated on save, etc), and provides very robust search capabilities without too much effort at all.