Mongo db stress test using different writeConcern

The aim is to determine how mongo performs using different writeConcern, which control the acknowledgment/quality of the write operations with various options, such as:
 ACKNOWLEDGED [default]
UNACKNOWLEDGED
JOURNALED
JOURNALED_SAFE
SAFE
FSYNCED
FSYNC_SAFE
WriteConern options are documented here: http://docs.mongodb.org/manual/core/write-concern/

Test results:  Total 200k documents are injected into 'user' collection using 4, 8 and 16 parallel threads
 

UNACKNOWLEDGED option is the fastest of all but not safe, on other hand FSYNC_SAFE is the most safe option but is the slowest of all..