2nd Xeon X5690 3.47GHz for Dell Precision T5500, How to Get?

Hi Everyone,

I have a Dell Precision T5500 with one Xeon X5690 3.47GHz. Now I'd like to add a 2nd Xeon X5690 to my workstation. Is it doable? I think I need a dual CPU riser for the additional CPU. Where can I get one and how to install the additional CPU into my T5500? I also wonder if dual CPUs can give a great boost on performance or not really.

Thanks!