Slow SSD Performance on iMac
Looks like a known problem with the SSD. OCZ has a firmware on their forum that will fix the issue. See the post "Changing SATA speed on your "3" series SSD." in this thread.


  This portion of the instructions only applies to OCZ "3" series SSD's - Vertex3, Agility3, and Solid3 - all sizes.
  Some SATAII motherboards, when used with one of the above drives will
  downgrade the drive to SATA1 speeds. We find this mostly on Nvidia
  chipset motherboards for PC and Nvidia chipset based Mac's. To resolve
  this, we have a tool that will set the link speed to be locked at
  SATAII and improve performance. This can be reversed when you update
  your motherboard/system so you can have the full SATAIII speed again.


Installing the firmware involves burning a Linux LiveCD so I hope you have a computer with the optical drive still in.