rows per insert  job execution time improvement N times faster
             1               102.7         N/A              1
            10                28.6      72.1 %            3.6
           100                15.6      84.8 %            6.6
           500                14.1      86.3 %            7.3
          1000                14.3      86.1 %            7.2
          5000                13.9      86.5 %            7.4
         10000                14.7      85.7 %            7.0

As you can read, performance improvement is huge. When inserting lines by block of 1000, the whole job is nearly 8 times faster. We also see that a too high value decreases performance. This is because the more we have high value, the more we use memory.

Warning: don't use a very high value for this new parameter because MySQL limits the size of the query in max_allowed_packet, which is 16M by default on my MySQL 5.0.45.

As a comparison, the bulk insert is still a lot faster. The same operation is done in 6.5 seconds.