SW VAR recommending XP64 over Vista?

My VAR has provided a spec for a 64bit machine as we'rehaving performance issues running COSMOS on large assemblies withour 32bit Vista Business machine. They recommended XP 64 over Vistastating that XP is much more stable.

We're running SW2008 and having read around the subject on theseforums, people seem to be having an easier time with Vista 64 thanXP.

Who do I listen to when deciding what is the best choice for us?The VAR who should know the software inside out? Or the users whoactually have the experience of A vs. B...?

Very confused now.
SolidworksAdministration