OPTIPLEX 960 Upgrade journey

Hi,

I got myself a new PC for work and I did not want to spend much, so I got one from the previous decade!

But now I realized that the speed is frustrating me. I have upgraded the ram and the hard and the graphic card withe magic of second hand shopping. But the processor is still a slug.

I tried figuring out what processor is compatible to Optiplex 960 motherboard, but I did not really understand how to find out.

Can somebody please let me know what is the maximum possible processor that I can hook up to this old fella?

The current speed is 3.0Ghz, and I think its not dual or quad.

Thank you