Regardless of the server version, MLCP does not support concurrent jobs if they are importing from/exporting to the same file.

In general, MLCP jobs will perform best by maximizing the number of threads in a single MLCP job. Before 10.0-4.2, each MLCP job used 4 threads by default. Starting in 10.0-4.2, each MLCP job now uses the maximum number of threads available on the server as the default thread count (you can read more about this change in the 10.0-4.2 release notes).