I must tell you, 320gb over a 1mbit line will gonna be hard, theoretically you can squeeze 324gb over this 125KB/s connection (8 kilobit = 1 kilobyte), but considering packet loss because of a lot of different factors you will probably get 200gb max, or have an unacceptably slow server (for an adult site).
If you want a decent server (for a very reasonable price) on a 100mbit burstable port, I recommend my
VibeHosting. Our dedicated servers are unmanaged but we do try to give our customers the best support we can, 24/7.