Whats the difference between a 3d design graphics card and a gaming card

The primary difference is drivers.

3D design cards have specialized drivers that don't do as well in games, but do very well in 3D design applications. The actual graphics processors are very similar.

That being said, you can't just switch up drivers to switch up how your card performs under different types of loads.

http://www.tomshardware.com/reviews/firepro-v3900-revie...

Yeah one would think that 3d CAD cards in need of much more vertex calculations than normal gaming cards and much less in the fillrate and pixel shader department. Perhaps the drivers tweak the cards' hardware to more vertex operations per second because the difference in Maya for example can be ten fold which is hard to explain by a simple driver tweak.

http://www.tomshardware.com/reviews/quadro-fx-4800,2258...

For the most part, the only difference would be the drivers.
As with above, workstation cards have drivers that are optimized for specific programs or tasks but are not necessarily optimized for gaming.

At a card level however, you can usually find some differences.
Workstation cards are designed to survive long periods of 100% utilization.
As such, they are generally clocked lower than their consumer counterparts and may have more robust voltage regulation onboard.