HP xw6600 - Expected performance increase with addition of 2nd CPU?

Our engineering department is set up with HP xw6600 workstations running WINP7 x64 and SW2009 SP2.1  The machines are outfitted with XEON 5410/5420 CPU's, FX1700 GPU's, 8GB RAM.  We use PDM so modeling takes place on our local machines.

What kind of performance improvements might be accomplished by adding a 2nd CPU at roughly \$250 a piece?  We're still kind of sucking wind after bumping our OS and RAM and aren't quite ready for new machines.

SolidworksAdministration