Here are some screen shots showing a comparison of Direct I/O versus non-Direct I/O options in ATTO benchmark.
First, as a baseline, I checked a single 40GB IDE Pata drive connected to a D975XBX2 motherboard. Notice that non-Direct is slower than Direct.
Next I ran the same comparison on the same computer, this time with four hard drives setup using RAID 5. This is with MSM 8.8 and the latest chipset drivers.
Notice that the non-Direct performance is much worse than Direct, and that non-Direct write performance is less than half of the single IDE drive.
Anyone else care to post some comparison results? Particularly from D975XBX2 boards?