Mine didn't have a fast enough CPU to be able to deliver 80/20 on my BT connection. However that was using pppoe which is resource-hungry so you may have better results on Sky as it's not pppoe.
Are you planning to use a router behind it then, and just use it as a modem? If so, which router?
As you bought it unlocked and then did a factory reset, I'm not sure what state it's in now, so I suggest you unlock it again.