Currently backing up my desktop machine before reformatting. I booted to a LiveCD and started using rsync to copy the contents over the LAN (rsync being resumable). However, it had a maximum transfer speed of 1.2MB/s, on a 100mbit LAN (so I should have gotten 8MB/s or so). I performed various tests, such as doing a netcat transfer and connecting machines direction (no router). I rebooted back into Windows, assuming it was a Linux driver issue, and experienced the same issue when using cwrsync and copssh. After poking around the driver settings, I Disabled "Large Send Offload" and rebooted, and now have transfer speeds of approximately 4.5MB/s.
This card also does Checksum Offload, which I'm tempted to disable, but I'll let it work overnight and the transfer should be complete by my morning.