This new driver seems promising so far (8.1u1 x64). I haven't had a connection drop since it was installed almost a week now. I did some stress tests as well, running torrent, downloading huge files on local network and from NAS which usually caused connection drops quite fast and repeatedly.
I'm not saying this has finally fixed the issue because I had my hopes up several times so far and eventually this issue always came back so far, but I doubt I ever had such a quiet period with the heavy use I did the last week.