What you need is a Network Switch which you connect to the existing "incoming" ethernet cable and this will give you additional RJ45 ethernet ports. These ports will run at your full network speed, which is dependent on the ports of the Router and Switch, i.e. 100Mbps or 1Gbps (1000Mbps). Obviously the available bandwidth will be shared by the active connections using the network.
If your "Hub" is what I think it is, i.e. a Network Hub, this is a less intelligent version of a Network Switch. A "Switch" sends packets of data to the correct IP address in the network, whereas a "Hub" sends all of the packets of data to all IP addresses in the network and lets the devices sort out what is theirs. This is less efficient and Hubs often have an LED to indicate when data collisions are occurring. The more collisions there are, the slower transfers of data will be.