Lots of other posts have highlighted possible cable/driver/adapter issues giving instability on a wired connection, so I'm not going to go there. There is one other reason why, in this particular context, your WiFi might appear more stable than using a wired connection.
As others have pointed out, unless you're running wireless-n at relatively short ranges and in a fairly "clean" RF environment then your wired connection to your router is almost certainly higher bandwidth than your WiFi.
This makes for much higher performance internal to your network, but you're experiencing instability over the end-to-end paths between you, FDEV's servers and any in-game peers you may have. The bottleneck in that path is almost certainly your uplink to your ISP. For inbound data, that's never going to be a problem for you as your internal network can suck down data faster than the downlink from the ISP can deliver it, whether its destination machine is on WiFi or wired. Too great a delta between the amount of data you can push to your router over a given pipe and the rate atwhich your router can upload it, however, can - under very specific circumstances - cause a problem.
In order to upload data incoming from a faster link over a slower one, your router must buffer it and send it on as fast as it can until it catches up and empties the buffer. So what happens if you connect a firehose to a bucket being drained by a drinking straw and the bucket fills up? Different routers handle this differently, some better than others, but in many cases - particularly on lowest-bidder consumer grade products - the extra incoming packets will just end up silently dropped so if this is your uplink to an E: D server or peer you'll see packet loss and disconnects.
This is a gross oversimplification of the potential situation, but accurate enough unless I'm talking to a fellow network administrator
