How much latency is too much for the game video to stay smooth??
it really depends on what you are doing. the more thingies need to be loaded from a server, the worse it gets. this is why i personally go exploring when on low connection speed. basically, after the advanced discovery scanner ping and the server request, which bodies need to be generated, there is nothing to load from the server.
also - just talking about my experience - you have to make sure that no other processes are eating up your connection speed, for exampel as a regular dropbox user, i have to disable dropbox when playing the game tethering.
anyway - probably you should take your machine once to a place with a good connection speed and play some hours, to get a feeling whether it is your connection or something else. it isn't like people playing over best broadband connection don't get desyncs, stuttering etc. pp. for exampel it is a known phenomenon by miners, that mining at the weekend take much longer, as there are a lot of server requests coming with it - no matter how good your connection is generally.
I'm no network specialists, and you'll find many good and more qualified tips on these forums - i also suggest you look at the official support site. they have a very good FAQ on how to increase your connection quality.
but i can tell you that you can play this game on very low internet connections
