Acronis True Image Home 11 Network Backup Is Slow

I support a small LAN with 7 Windows 7 64-bit desktops for a local charity.

All the desktops have Acronis True Image Home 11 (ATI11) installed and are configures as a HomeGroup. I have been doing an incremental image backup over the network using ATI11 to one of the desktops but lately speed of the backups has become unacceptable.

For a specific example, Two of the desktops are Core I7 machines with GBit network interfaces connected through a GBit switch.

a) If I backup one to the other using ATI11 the backup will take 4-6 hours with network utilization at 3-5%.

b) If I backup the SAME system to its secondary HDD using ATI11 (a local backup) the backup takes about 2 hours.

c) If I then use a simple COPY command to copy the large ATI11 TIB backup file (30-50GB) from the SAME system to the SAME target system the network utilization varies from 25%-60% and the copy takes a, relatively speaking, small amount of time.

Note I get the same results for source systems which only have a 100MB network card except that during the COPY test they use 80-90% of the available network speed.

changing the network cards settings, IPV4 Checksum Offload for example. I tried that and it immediately "broke" the HomeGroup network connection. Question: Why will ATI11 not use more of the available network speed? Neither the source system nor the target system is CPU bound during the ATI11 backup, network or local. Aside from Norton Antivirus there are no other non-MS apps running. Disk Queue Length is not excessive.