I have ~10mbps upload here in the US, and my backup was looking to take about a month for about 3ish TB of data. One thing that helped is that with default settings of only 1 backup thread, the Windows client was unable to saturate my upload bandwidth. Upping it to 4-6 threads allowed it to keep enough data moving to actually saturate my upload bandwidth and brought my backup down to like a week.
Hurray for Canadian internet.