As K.C.Leblanc said, get a gigabit switch, connect all of your PCs to it, and then connect it to a single LAN ethernet port on the router. Even a cheap Dlink (~£45) will be good enough, as you will not see 1Gbit between 2 machines, because your hard drives will be slower than the network. (A fast SSD at each end with read and write speeds of 200MB/s would max 1Gbit ethernet, but a fast traditional hard drive ~100MB/s won't).
Also do not enable jumbo frames, this will cause a drop in performance when trying to upload content to the internet.