I verified that the maximum overall speed that can reach one or more simultaneous downloads from omv to local, is equal to about 11Mbps. The download of a 4GB iso file proceeds at 11Mbps. With the simultaneous download of the same file, on multiple clients, the speed is shared between the clients, but the overall speed is always around 11Mbps. Where does this speed come from? Does it depend on the omv hardware configuration or does it depend on the network?
It comes from whatever is the bottleneck. It might be the network. Or some part in the network. Or slow disk i/o. Or something else.
OMV has no built in speed limits. It is your hardware, in combination with the software, that sets the speed.
From your description it could be the network that is your bottleneck.
11Mbps = you are limited to 100Mbit not 1 Gbit
check you cable and be sure that use cat 6 cable