In my case, a client had 2 external RAIDs, 2 different brands, 1 Firewire 800 the other firewire 400, Windows 7 Ultimate X64. The speed was terribly slow. I first installed the {Legacy} drivers for the IEEE devices and it did improve a little but barely. With a little digging I found a solution in the External Drives Properties.

The default Windows settings for FireWire-connected drives can reduce your External drive performance by as much as 90%. This problem is easily corrected, just follow these instructions:

1. Open “My Computer” or “Computer” from your (Start) Menu or Button.
2. Right-click the external Hard disk drive from the list and select “properties”
7. Click the “Hardware” tab.
8. Highlight the drive your having problems with from the drive list and click on “Properties”.
9. Click on the “Policies” tab.
10. You will see two radio buttons – “Optimize for quick removal” and “optimize for performance”.
11. If not selected, select “Optimize for performance” and click on “OK”. If running Vista or Windows 7 also check “enable write caching on the disk”.
12. Click on “OK” and exit.

Lighting speeds should now be reached.
This problem affects XP, Vista and Windows 7. It may improve performance for any drive connected via FireWire.

Good Luck!