FC5 Disk performance issues with HT1000 chipset

I have 4 machines with the ServerWorks HT1000 chipset and a WD SATA drive. 3 of them are running FC4 with the HT1000 kernel modules added in by me, and I just installed FC5, which doesn't need the ServerWorks drivers, on the 4th. I ran a loader program to build the data files on the FC5 machine and noticed the disk speed was WAY lower than the FC4 machines, like 1-5th the speed of the FC4 machines. Here's an iostat from each machine with the load process running:

FC4:

Device: rrqm-s wrqm-s r-s w-s rsec-s wsec-s rkB-s wkB-s avgrq-sz avgqu-sz await svctm %util sda 0.00 508.97 0.00 1029.90 0.00 12310.96 0.00 6155.48 11.95 0.88 0.86 0.85 87.41

avg-cpu: %user %nice %sys %iowait %idle 0.33 0.00 0.50 13.33 85.83

Device: rrqm-s wrqm-s r-s w-s rsec-s wsec-s rkB-s wkB-s avgrq-sz avgqu-sz await svctm %util sda 0.00 782.94 0.00 1744.15 0.00 20216.72 0.00 10108.36 11.59 0.96 0.55 0.55 95.92

And now FC5:

Device: rrqm-s wrqm-s r-s w-s rsec-s wsec-s rkB-s wkB-s avgrq-sz avgqu-sz await svctm %util sda 0.00 117.33 3.33 261.33 112.00 3029.33 56.00 1514.67 11.87 1.01 3.82 3.78 100.00

avg-cpu: %user %nice %system %iowait %idle 1.00 0.00 0.33 48.84 49.83

Device: rrqm-s wrqm-s r-s w-s rsec-s wsec-s rkB-s wkB-s avgrq-sz avgqu-sz await svctm %util sda 0.00 215.28 3.65 258.80 108.97 3795.35 54.49 1897.67 14.88 1.01 3.85 3.72 97.67

Java version from both machines: java version "1.5.006" Java(TM) 2 Runtime Environment, Standard Edition (build 1.5.006-b05) Java HotSpot(TM) Server VM (build 1.5.006-b05, mixed mode)

As you can see, the FC4 box was writing at 10 MB-sec while the FC5 boxwas writing at ~2 MB-s. It's the same version of the software and the same version of the JVM. I've tried changing between IDE and MMIO mode in the bios but there's no change in write speed. The hardware across all machines is identical, each machine has a dual-core Opteron FC5 had been running FC4 and getting the fast writing speeds before FC5 was installed.

Has anyone else encountered this problem, and does anybody know how to solve it?