Turning off the hub constantly actually wont help - they tend to stabilise to their best speed over a period of time. I had a new Hub installed today, and although the speed was good as soon as it started it only really got a reliably fast (top-speed for my connection) download after 20-30 minutes.
Generally all modems are the same - there is a fair bit of handshaking that goes on between the modem and the Virgin/BT/whoever's kit to determine what the line speed actually is and they gradually work up to it so that they can achieve a nice, reliable and stable connection.