So I just noticed that after installing Mavericks, I get about 70 MBps when copying files from my Windows Vista machine that's on the same network. Before, I maxed out at 50 MBps. The iMac, Windows Vista PC, and switch are all gigabit. However, I do get errors when copying more than 1 file at a time. "The operation can't be completed because an unexpected error occurred (error code -51)"