I think your other post has the right idea ... Router/Modem at the socket then a Cat5e/Ethernet cable to a small 8 port switch from where you can route to the various devices. Switches £10 to £20 and the investment will be worth it.
By using a twisted pair, you may recover 100 or 200 kbps but certainly not the 700kbps you loose. I would guess that the reason for that is local noise which twisted will partially mitigate but there will still be a loss.
M H C
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