The FirePro graphics products are all based off Radeon GPU counter-parts. For example, the FirePro V8800 is based off the Radeon HD5870. However, the FirePro products offer significant performance improvements in programs like Maya and Autocad, because tweaks to the hardware and (more importantly) drivers are done. The "3D work" involved with Solidworks is entirely different than the "3D work" invovled with playing games. FirePro cards also cost a lot more.
I have played many games quite happily with high-end FirePro graphics cards like the V8800, but that's because they were still high-end Radeon GPUs powering them. I would expect the games to play well with something based off a Radeon HD5870. However, it would be silly to pay the price of a V8800 for gaming, compared to what an HD5870 costs.
I would recommend purchasing a high-end Radeon graphics card to statisfy his gaming needs, and I suspect it'll have enough power to work well for his work-related applications. If his work-flow and productivity needs demand the FirePro product than that would justify the cost of the FirePRO card. You could likely spend as much as the cost of a high-end Radeon card on a FirePro card that will suit his needs, but then that FirePro card may be too low-end for gaming. At that point, consider 2 computers may be the solution.
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