I've got the opposite situation. My USB transfer speeds are fast but FireWire 800 is horrendously slow and eSATA doesn't work! I attempted to transfer 40Gb of data yesterday to an external drive and the estimated time by FW800 was "More than one day", but only about 35min by USB.
The same external drive connected to my MBP by FW800 imported a 16Gb video in 30 min, so I know the drive is fine and the problem must be Windows 7 drivers.