Apple Mac Pro 5.1"Quad Core" 2.8 Server Mid-2010 - A1289 - 2314-2 What the best customisation?

I guys,
I just bought an Apple Mac Pro 5.1"Quad Core" 2.8 Server Mid-2010 - MC915LL/A - A1289 - 2314-2 on eBay, and it coming with this specs:

Intel Xeon 2.8Ghz (Quad Core) W3530, 500GB HDD, 8GB DDR3, Registered RAM, ATI HD 2600

I'm looking for the best performance is possible on this machine and I need your help. As we can see here http://www.everymac.com/systems/app...d-core-2.8-mid-2010-nehalem-server-specs.html I can make a CPU upgrade for two 2.93...

Apple Mac Pro 5.1"Quad Core" 2.8 Server Mid-2010 - A1289 - 2314-2 What the best customisation?