MySQL has a few engines that still have a database level lock ( MyISAM, MEMORY ) and those generally preform better for unbalanced loads ( i.e very read heavy or very write heavy )
Do you have any source for this? While logic suggests that they should (but perhaps only very slightly) I think InnoDD has got a lot of more optimization work than any other engine.
A benchmark from Oracle shows InnoDB as being much faster on a read-only workload.
