Worth Upgrading Processor?

I just started at a new company and the computers are a few years old.  From the last place I was at they seem pretty slow.  I ran the punch holder benchmark and got 124 seconds, not that good.  We use Solidworks for design with some large assemblies and drawings but no animation or FEA or anything like that.  We also use Pro-e for design.  Here are my computer specs:

Dell T5500

Windows 7, 64 bit

Intel Xeon E5503 @ 2.00 GHz

12.0 GB RAM

250 GB Hard Drive

ATI FirePro V7800

From everything I've read the processor is the most important for the type of work I do and it seems this processor is pretty old.  I asked Dell to quote me the best new processor that would fit into the current machine and they quoted me a E5620 @ 2.4GHz for \$450.  Is this worth it?  Would I see a 25% or more improvement?  Or would I still be better off pushing for a new machine?

Any other ideas on how I could make this computer faster?

Thanks,

Mike

SolidworksAdministration