The only benefits of SATA I or II interface technology (currently) are the thinner cables and its hot swappability. Also, there are no jumpers to set for a master/slave installation, since all SATA drives are masters.
My SATA I Seagate 80 GB 7200.07 reads at 58 MB/s, for example, so you are doing better than me, because you have a larger drive (yours has more recording density for a given area).
That's why your speeds are faster than mine; it is not a result of SATA II vs SATA I.
-Bob