From what I gather the issue was something to do with the "profile" my account was set to on AGL's side - it seems that these profiles differ depending on whether the account is set to a public or private IP, and there was initially no option that the technician could choose to enable gigabit with a public IP, though there were a few options that he wasn't sure about, so he had to consult with his colleagues to find a solution - which he was able to by the end of the day. It's also worth noting ...