You'll see a huge jump in performance.
To make you feel better, that $189 sale was for the PCI-E version of the card. Since you're running a 9600pro I'm assuming you have an AGP slot.
Oh...Asrock dual sata...so you have both.
Okay, feel bad.
You might want to wait until we get some more benchies out of the 6800GS AGP. Some results have been really good with unlocking pipelines, up to 5400+ on 3dMark05. The PCI-E has higher stock speeds and looks to overclock extremely well, but early results are that you can unlock to 16/6 on the AGP version.
-z