Difference between 6.2 and 7.0 Adaptec 39320D - 7.0 performing less

Goodevening lists,

I am toying with Freebsd 7 to see if it will and how it runs on my new Asus 
M2N mainboard. One of the things I noticed is that when running 
7.0-Current-200704 the throughput of the SCSI drive seems halved. When 
running 6.2 throughput is doubled/normal.

Throughput is measured with the following command.

dd if=/dev/zero of=/usr/test
where /usr resides on da0s1f

On 7.0 I get about 33MB/sec
On 6.2 I get about 69Mb/sec

I did not make any changes, installation is fresh from CD with Minimal as 
distribution.

As the NIC is not yet supported by Freebsd and I haven't got it working yet 
(need to get a supported nic in, hopefully tomorrow or the day after) I can 
only provide the below information. I had to type it reading it from another 
console :( (this also means that I cannot CVS atm)

If I need to raise a PR or something else for this please let me know, as I am 
new to this process. If you require more information please let me know as 
well, I am happy to provide.

Kind regards,

Patrick Gelsema
__________________________________

System Details:
mainboard: Asus M2N
processor: AMD Athlon 64X2 4800+
memory: 2GB
chipset: NVidia MCP6

logs read from console when running: 7.0-Current-200704

ahd0: <Adaptec 39320D Ultra320 SCSI adapter> port 0xe800-0xe8ff,0xe400-0xe4ff 
mem 0xdd7fe000-0xdd7fffff irq 16 at devuce 10.0 on pci1
ahd0: [GIANT-LOCKED]
ahd0: [ITHREAD]
aic7902: Ultra320 Wide Channel A, SCSI Id=7, PCI 33 or 66Mhz, 512 SCBs
da0 at ahd0 bus 0 target 4 lun 0
da0: <SEAGATE ST336753LW HPS2> Fixed Direct Access SCSI-3 device
da0: 160.000MB/s transfers (80.000MHz DT, offset 63, 16 bit)
da0: Command Queueing Enabled
da0: 34732MB (71132960 512 byte sectors: 255H 63S/T 4427C)

logs read from console when running: 6.2 Release #0

ahd0: <Adaptec 39320D Ultra320 SCSI adapter> port 0xe800-0xe8ff,0xe400-0xe4ff 
mem 0xdd7fe000-0xdd7fffff irq 16 at devuce 10.0 on pci1
ahd0: [GIANT-LOCKED]
ahd0: [ITHREAD]
aic7902: Ultra320 Wide Channel A, SCSI Id=7, PCI 33 or 66Mhz, 512 SCBs
da0 at ahd0 bus 0 target 4 lun 0
da0: <SEAGATE ST336753LW HPS2> Fixed Direct Access SCSI-3 device
da0: 320.000MB/s transfers (160.000MHz DT, offset 63, 16 bit), Tagged Queueing 
Enabled
da0: 34732MB (71132960 512 byte sectors: 255H 63S/T 4427C)