Depends on the model, but really there is no difference for those portions of CS5, only Premiere and After Effects benefit from the CDUA based GPU acceleration in CS5, and then it's only certain models, in which case unless you're a pro it's best to get a GTX285 instead.
But for all of the components you're using they use OpenGL acceleration and are available to both vendors.
The only consideration would be if you have a truely high bit depth monitor that support true 12bit per channel colour, that would be the only reason to get a workstation card (FireX/Quadro) as they support up to 16bit per colour channel, whereas the gaming models are 10 per channel usually and 12bit (with 10bit corrected output) for the best models via HDMI.
But if you're no using a specialized monitor then don't waste your money on a FireGL/FirePro or Quadro card, get a quality, low power consumption, large memory, cool 'n' quiet mid-range card (something like the HD5770 or lower or the GTS250). A nice card for a cool and quiet rig would be the new HD5550 with the passive heatsink, but it s a bit slower. I prefer the HD5K series because of the better sub-pixel support and the better colour depth support on DP and HDMI, but even then it's not as good as it could be (limited output on HDMI below the level of GPU support).