Using 2 Different xeon processors in Z800 Workstation

Hey everyone ,

I have a z800 curretly running with 1 processor Xeon X5660 which is 12 MB cache 2.80 GHZ running with 16GB of ram.

My question here is can i upgrade my work station and add another processor which is Xeon X5560 Which is 8MB Cache .

Or both processors must be same model.

Thanks.