i just look it in the Task Managers network tab. I have tested with some program (don't remember the name) that my hdd is capable to transfer averagely 7MB/s, so the bottleneck isn't my hdd. the cable is 4m long, so it shouldn't lose that much of it's efficiency. i don't use a twisted pair cable, it's a BNC cable.
--edit edit:
i tried transferring small files (about 4%) and a 400mb chunk (around 30%), and both machines' hdd:s are defragged just a couple of days ago.