Search in the Administration forum for advice on hardware. And ask this question there, as it is the main focus for hardware questions.
I don't remember seeing much information about quiet workstations. Most people are more worried about speed than noise levels.
ATI video cards seem to offer the most bang for the buck right now. But there is still a lot of pushback from people who have been burned by ATI support and won't switch from Nvidia. I haven't seen many actual complaints from new ATI card owners.
For me the high end video cards are overkill, but we don't do large assemblies. We may have assemblies with between 1K and 2K parts, but most of them are capacitors and resistors on the PCA, so they don't require much computing power to draw. People with truly large assemblies seem to find the high end cards worth the money.
SolidWorks has historically not taken much advantage of multiple cores. Drawings can use one core per view for some processes. Some Surface features use more than one core (surfacing often uses a lot of bodies.) Rendering uses multiple cores. Flow Simulation uses multilple cores. Simulation might, but I'm not sure what the limitation are. Having said all that, I'm not on the 2013 Beta testing so I don't know if 2013 will change any of that and I couldn't tell you if were, because I would be under NDA. I haven't heard any rumors suggesting that 2013 will make any big changes in processor usage.