According to Netflix, the Internet speed you'll need for downloads is as follows: For any streaming at all, you'll need a minimum of 0.5 megabits per second (Mbps), but Netflix recommends 1.5 Mbps. For DVD quality, you will need 3.0 Mbps. For HD quality, you will need 5.0 Mbps.
Sky Go suggests 2 Mbps is required for their service.
So assuming it is fairly consistent, up to DVD quality should be fine.