upgrade MacPro 3.1

Hello guys,
I have 3 catalyst V4 on MacPro (2008) with GEFORCE 8800 GT.
Is there any graphic card for upgrade my Catalyst?
Thank you

MP

Used Quadro 4000 might be a good option
Also the HD7950 might work, depending on the OS you are using.

Thank you mlorenz,
The OS X, now, is 10.6.8 but I want to try with Maverick if the machine supports it well.
Someone has tested these cards with Catalyst V4 Mac Pro 3.1 ?