Some people write to us with really low speed figures in the range of 15-30 MB/s, or even lower, on servers from which you should expect much more and connected via decent NICs and switches to peripheral devices.
We have found that in many cases, those poor figures are related to overloaded servers.
Virtualization allows to set up tenths or even hundreds of VMs per server, but that gives many people the wrong idea that you can stretch that forever. Virtual machines make use of the underlying hardware anyways. If you have ten active VMs in a production server, you are short of RAM because of that and (c)XSIBackup-DC has to "beg" CPU time and bandwidth to the system, you can't expect things to run fast.
Size your server in an appropiate way, always leaving some free resources, otherwise you will be just pushing some new stuff into the room for some other to be pushed outside and scratching your head wondering what went wrong.