EXPLAIN :
> db.loadtestsharded.find({ "_id" : ObjectId("4e5677fcfb2317a3d2860220"), "hash" : 19051072}).explain()
{
        "clusteredType" : "SerialServer",
        "shards" : {
                "127.0.0.1:27021" : [
                        {
                                "cursor" : "BtreeCursor hash_1__id_1",
                                "nscanned" : 1,
                                "nscannedObjects" : 1,
                                "n" : 1,
                                "millis" : 0,
                                "nYields" : 0,
                                "nChunkSkips" : 0,
                                "isMultiKey" : false,
                                "indexOnly" : false,
                                "indexBounds" : {
                                        "hash" : [
                                                [
                                                        19051072,
                                                        19051072
                                                ]
                                        ],
                                        "_id" : [
                                                [
                                                        ObjectId("4e5677fcfb2317a3d2860220"),
                                                        ObjectId("4e5677fcfb2317a3d2860220")
                                                ]
                                        ]
                                }
                        }
                ]
        },
        "n" : 1,
        "nChunkSkips" : 0,
        "nYields" : 0,
        "nscanned" : 1,
        "nscannedObjects" : 1,
        "millisTotal" : 0,
        "millisAvg" : 0,
        "numQueries" : 1,
        "numShards" : 1
}

CORE AFFINITY ASSIGNED (1 core per mongod, 1 core loadtest/mongos) :
Connecting to 127.0.0.1:27017 using 8 threads
Testing save operation, normal		 : 40690 operations/sec
Testing save operation, sharded		 : 29617 operations/sec
Added 1000 elements to candidate list for normal queries
Added 1000 elements to candidate list for sharded queries
Determining shard distribution of sample documents :
Shard 0:346
Shard 1:331
Shard 2:323
Testing find operation, normal		 : 14841 operations/sec
Testing find operation, sharded		 : 17362 operations/sec
Testing update operation, normal	 : 10167 operations/sec
Testing update operation, sharded	 : 8564 operations/sec

NO CORE AFFINITY :

Connecting to 127.0.0.1:27017 using 8 threads
Testing save operation, normal		 : 46881 operations/sec
Testing save operation, sharded		 : 53581 operations/sec
Added 1000 elements to candidate list for normal queries
Added 1000 elements to candidate list for sharded queries
Determining shard distribution of sample documents :
Shard 0:321
Shard 1:332
Shard 2:347
Testing find operation, normal		 : 20840 operations/sec
Testing find operation, sharded		 : 20679 operations/sec
Testing update operation, normal	 : 12413 operations/sec
Testing update operation, sharded	 : 8897 operations/sec