I know this is an old thread but Converter 5.0.1 b875114 still has the same issue. By default, SSL is enabled on the Converter in the "converter-worker.xml" file. When I turned off SSL and restarted the VMware converter worker service, my rate went from 140KB/sec to 45MB/sec. I wish that VMware would fix this issue (it wasn't like this in previous versions, i.e., 3.5, 4.x). Even for secure transfers needing SSL, 140KB/sec is unacceptable.
Thanks for the help!!!