The SLI probably won't help you with Solidworks, but it should run fine. I've seen it run OK on a geforce 6800GT. The workstation will probably work better if you have complex assemblies due to the better workstation video cards.
I got an XPS at work about a year ago to run AutoCAD, for the same reason. It was cheaper than their workstations and you get more as well. I was actually surprised how nice of a machine it was. The only downside is that the case is massive. But it's prewired for a bunch of extra drives, and is really a sweet setup.