Here is a shot of my Crucial M4, in an i5-2410M SB laptop and attached to Sata III port.
Look at the Nrs. (Lesen = Read and Schreiben = Writes.
Seq read is 500 MB/s (Would saturate SATE II - SO what, Sequencial has little impact. The 4K-64K thread read is right at the saturation point.
All others are well below sata II's cap. and it is the 4K read/writes that is most important.
http://i55.tinypic.com/nbq5xj.jpg
I just finished installing a 120 gig agility III in my wife's computer (on SATA II). This was a OS +program drive in my computer and on SATA III
THERE IS NO difference in performance with this drive, Granted it is not the best example, as the Better SSD would show a small decrease in performance, JUST NOT as much as many think.