How did you manage that ? Faster than any HD's i've ever heard of.
Easy: turn off NAS device, take two old drives out of the NAS device, remove old drives from their clips, put two new drives into the clips, put new drives into the NAS device. Easiest hardware upgrade I ever did. Note tongue in cheek in diagram A above ;-)
Seriously, if you want to move a lot of data quickly, pushing it down an Internet connection is not necessarily the way to go unless you have major bandwidth to spare. It can be much more cost efficient to just put it on a disk of sufficient size and move it physically yourself, or by hiring a courier service.
This is how, for example, some of the post production work was done in the "Lord of the Rings" films, in London. They put the data on an iPod and somebody carried it to where it was needed.