Thinking of wiring a ethernet cable through the walls up to my bedroom and then connecting it to a rj45 plate. Although i have heard that the longer the cable the worse your internet gets, is this true? ill be using about a 30 metre cable.
If you're connecting to the LAN side of the router then 30m of cable will make no difference.
If you're talking about a phone line extension for the WAN side of the router then there's a chance it'll reduce your sync. It really depends on how good a job you make of it.