20Mbps on a 20metre Cat5e cable suggests something is wrong at one end or teh other. That cable should be capable of handling Gigabit connections.
I would suggest installing a pair of RJ45 sockets next to the router and another at te remote location and use Cat5e cable to connect them both. Then a set of short patch leads at each end.
If you can get the cable in easily it will be cheaper and more efficient than plugs.
M H C
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