Prebuilt Optiplex Upgrade

[thepcnoob02]

I currently have a Dell Optiplex 960 with a Core 2 Quad Q9400 and was wondering if there is any CPU upgrade path. I already have a GPU and a 600w EVGA power supply

 

[freercurse]

Intel Pentium 4 Extreme Edition? perhaps im really not to sure.
I cant recommend upgrading such an old system though

 

[rgd1101]

http://www.userbenchmark.com/System/Dell-OptiPlex-960/527
Core2 Quad Q9650