IDE performance slowdown in 2.5

With 2.5.47, I get 22mb/s using hdparm -t /dev/hda, and close to 40mb/s when running 2.4.x
Is this at all expected?
Info from hdparm:

[13:19:08] root@debian:/proc# hdparm -v /dev/hda
/dev/hda:

  multcount    =  0 (off)
  IO_support   =  1 (32-bit)
  unmaskirq    =  1 (on)
  using_dma    =  1 (on)
  keepsettings =  0 (off)
  readonly     =  0 (off)

readahead = 256 (on)
geometry = 50765/16/63, sectors = 117231408, start = 0

[13:18:51] root@debian:/proc# hdparm -i /dev/hda
/dev/hda:

Model=ST360021A, FwRev=3.05, SerialNo=3HR01F5W
Config={ HardSect NotMFM HdSw>15uSec Fixed DTR>10Mbs RotSpdTol>.5% } RawCHS=16383/16/63, TrkSize=0, SectSize=0, ECCbytes=4 BuffType=unknown, BuffSize=2048kB, MaxMultSect=16, MultSect=off CurCHS=4047/16/255, CurSects=16511760, LBA=yes, LBAsects=117231408 IORDY=on/off, tPIO={min:240,w/IORDY:120}, tDMA={min:120,rec:120} PIO modes: pio0 pio1 pio2 pio3 pio4
DMA modes: mdma0 mdma1 mdma2
UDMA modes: udma0 udma1 udma2 udma3 udma4 *udma5 AdvancedPM=no WriteCache=enabled
Drive conforms to: device does not report version: 1 2 3 4 5

Info from dmesg:
ide: Assuming 33MHz system bus speed for PIO modes; override with idebus=xx
VP_IDE: IDE controller at PCI slot 00:07.1
VP_IDE: chipset revision 6
VP_IDE: not 100% native mode: will probe irqs later
ide: Assuming 33MHz system bus speed for PIO modes; override with idebus=xx
VP_IDE: VIA vt82c686b (rev 40) IDE UDMA100 controller on pci00:07.1

     ide0: BM-DMA at 0xd000-0xd007, BIOS settings: hda:DMA, hdb:pio
     ide1: BM-DMA at 0xd008-0xd00f, BIOS settings: hdc:DMA, hdd:DMA

hda: C/H/S=28733/16/255 from BIOS ignored
hda: ST360021A, ATA DISK drive
hda: DMA disabled
ide0 at 0x1f0-0x1f7,0x3f6 on irq 14
hdc: RICOH CD-R/RW MP7163A, ATAPI CD/DVD-ROM drive
hdd: CD-ROM 32X/AKU, ATAPI CD/DVD-ROM drive
hdc: DMA disabled
hdd: DMA disabled
ide1 at 0x170-0x177,0x376 on irq 15
hda: host protected area => 1
hda: 117231408 sectors (60022 MB) w/2048KiB Cache, CHS=116301/16/63, UDMA(100)
hda: hda1 < hda5 > hda2 hda3
hdc: ATAPI 32X CD-ROM CD-R/RW drive, 2048kB Cache, DMA

(Why does it say DMA disabled there [for hda], yet hdparm says its enabled? I checked that there is no init script changing settings on the drives.)

Forgot to mention, the filesystem is ReiserFS 3.