Need help specifying a SW computer

I'm currently running SolidWorks 2013 on a Dell Precision M6700 with a core i7 2.6 GHz processor, 16 gig ram and a NVIDIA Quadro K3000 video card.  We have a second laptop similarly sized with a NVIDIA Quadro K4000 video card.  Both machines are running slow when we are working on larger assemblies. 

We're considering purchasing a desktop and I'd like to get an idea of the best video card to run.  We've been told by our VAR that we should be running a 3 GHz processor or better, 16 gig of ram but their help on video cards has not been helpful. 

I'm looking for anyone who can suggest a better video card option than we have.

Thanks in advance,

Judd

SolidworksGeneral