Hardware :: SATA / PATA Fake RAID Highpoint 1640 Slow In Writing

I've been, for some years, an happy user of Highpoint HPT374 based RAID cards, using RAID 5 with decent performances (constantly around 90 MB/sec in read, and 60 MB/sec in write ). Old Athlon mobo , with 2.6.8 kernel. Now the mobo is dead, so I've got an Asrock A330GC (dual proc with 4giga ram), installed Debian with kernel 2.6.26 and moved the controller and disks , and the performances have dropped to a painful 9 MB/sec in write, measured with dd of a huge file (interrupted with kill -USR1 [pidof dd]).

Read performances are still around 90MB/sec, using hdparm -t , repeated many times , figures are constantly around 90MB/sec. I suspect some libata issue , in old kernel the raid was seen as hdb, now is sdb, some driver(s) of the PATA disks may be responsible. I've used the driver, from Highpoint v2.19 , the latest driver is broken (causes kernel oops during format of raid), I've informed Highpoint.

Here some info :
hdparm -i /dev/sdb :
HDIO_GET_IDENTITY failed: invalid argument .

lspci :
00:00.0 Host bridge: Intel Corporation 82945G/GZ/P/PL Memory Controller Hub (rev 02)
00:02.0 VGA compatible controller: Intel Corporation 82945G/GZ Integrated Graphics Controller (rev 02)
00:1b.0 Audio device: Intel Corporation 82801G (ICH7 Family) High Definition Audio Controller (rev 01)
00:1c.0 PCI bridge: Intel Corporation 82801G (ICH7 Family) PCI Express Port 1 (rev 01)
00:1c.1 PCI bridge: Intel Corporation 82801G (ICH7 Family) PCI Express Port 2 (rev 01) .....