Took me 29 hours to do about 550GB (1GB connection aswell). So you're doing better than me!
I gave the DNS-323 away in the end due to this.
Saying that I got about 11mb/s from my main PC with jumboframes, but 16mb/s from my server (which replaced the 323, my desktop to server without jumboframes is 65+mb/s) without jumboframes. I found it too inconsistent for me.
Although, the person I have given the DNS-323 to only really uses it to read (the files I put on), and will only be writing to it occasionally so it meets their needs. If you do a lot of big transfers like I would be doing though it's not practical.