Comment below is specifically for SolidWorks 2010/2011 and Radeon cards, but may apply to future versions of SolidWorks.
I've built a workstation for a coworker using a gamer card, HD 6870 specifically, for SolidWorks at work, and it runs perfectly fine. I've also tried forcing equivalent firepro driver onto it but found no appreciable difference in benchmarks for those wondering. Additionally, as far as I can tell by examining published online benchmarking results with AMD gamer/pro cards, SolidWorks does not seem to employ GPGPU to assist in computations (unless 2012 version changed that, which is doubtful), thus a pro card does not make it run faster (more on this in next paragraph). Instead SolidWorks appears to only use the GPU for display purpose. The firepro driver does give you a RealView feature, which is realistic shadow/reflection that is neat to look at but doesn't do you any good in terms of productivity increase.
More so, SolidWorks is not multithreaded either outside of using extra threads for UI. When you are designing/rebuilding parts/geometry, single threaded performance is the biggest factor in how long it takes. To demonstrate, you can head to
www.solidmuse.com for rebuilding benchmark (e.g. the punch holder rebuild @
http://www.solidmuse.com/benchmarks/punch_holder_results.php) and you'll see clearly cpu speed is the primary factor in rebuild time, not GPU (I'm assuming you're not memory limited of course).
So why do SolidWorks insist on pro cards? My guess is that it is primary motivated from a technical support and validation perspective. First, pro cards have dedicated resources allocated for optimization and validation, specifically for bug fixes and stability reasons that this may be preferred. Also, for product like SolidWorks, it is much easier for them to test relatively few workstation configurations (e.g. from Dell and other big builders) and say if they work than it is to test the myriad of other possible configurations that a gamer might use. This is also why they offer recommendations of tested specific workstation builds.
Of course at my work place, the IT department's recommended system setup is usually quite... conservative and a year or two out of date hardware wise. Thus for less money I can build a faster and more efficient system, so if I can get away with it I do it from time to time(Our IT give us some nasty remarks/looks when we don't follow their rules...). Anyway, personally if you are decent with computer, know how to keep things updated, know how to rollback drivers (even better backup old GPU drivers) when issue arises, then I don't see why you cant save some money. However if the company is willing to shell out for a nice Dell Workstation with 24/7 support (or other brand) by all means.