I don't know if this helps, but I had problems with large file transfers between Win 7 and Win XP. What worked was to set each computer's network card speed to 100Mbps/Half Duplex. I tried "Auto", 100Mbps/Full Duplex, 10Mbps at both Half and Full Duplex with no success. The computers are connected to a 100Mbps switch/router. I haven't noticed any side effects with the Half Duplex.
If I recall correctly, the slow transfer was in only one direction, and may have also have been affected by which computer "pulled" files from the other computer, or which computer "pushed" files to the other computer. Unfortunatly I don't remember the details.
Also, please note that I'm not running AC on these computers.
