How long is a piece of string?
I have seen 6Mb a second and 40Mb a second over a 100Mb WAN link using the same kit on different days. If the link is busy you are out off luck, talk to the WAN team...
700mb in 4 hours does not sound good however. It works out to be dial up speeds.
You could try pktt trace and look at the network packets in wireshark. I had a snapmirror problem with low throughput which was caused by 'windowing' issue on the WAN and it was not until I proved the problem that the WAN team agreed that MAYBE something was wrong with the WAN. Then it was fixed magically.
The commands {run for only a couple seconds or the logs are to big}
pktt start all -d /etc/log
then
pktt stop all
