Looks like it is using udma2 instead of the newer udma5 or udma6 modes. I'm not familiar with Debian but you may want to find out about that chipset driver. It is usually in the kernel or in as a module. I'm not sure about how Debian is set up. Sorry.
This is what my timings are:
root@smoker / # hdparm -tT /dev/hda
Timing cached reads: 1348 MB in 2.00 seconds = 672.76 MB/sec
Timing buffered disk reads: 170 MB in 3.00 seconds = 56.58 MB/sec
root@smoker / #
Your should be somewhere around there, at least better than what you have now for sure. That drive should be much faster than that.
Anybody more familiar with Debian and how they have their stuff set up??