RE: http://docs.mongodb.org/manual/administration/production-notes/#manage-connection-pool-sizes

The following statement should probably just be deleted:

When using the WiredTiger storage engine, the number of incoming connections to Wired Tiger should be less than or equal to the number of cores available on the machine.

The connections talked about are two different things. I don't think there is anything the user can do about the number of internal threads to the storage-engine (though perhaps this should be checked?). Either way it certainly has no relation to client connection-pool sizes.