I've just moved house and I've gone from a stable 60Mbps download to a slightly ropey 3Mbps download, and the game is lagging like buggery now. Is there a particular speed that makes the diffference between playable and not?
First you talking about choppy unit movements and so? This might is might be related to your internet connection, but actually more important bandwidth between you and game server. I'm not sure yet (this never confirmed by Uber), but I'm thinking that servers have some strict bandwidth limitation per player, so currently after some point it's doesn't mater what internet connection speed you have.
Yes, choppy movements, delays in input, all that jazz. According to Speedtest my ping has dropped from ~18 to ~70ms, and I don't recall the upload but I think it's around 1Mbps now.
Actually if you have input lag it's most likely high latency to server, did you tried different server region?