I haven't used Maya in years... But at the time the problem was that a game card like a GTX didn't have the features in the drivers that Maya needed. If you used the 3D brush with the Fur tool, or Artisan, or particle effects, then the brush would smear all over the screen and you couldn't see what you were doing, it was a total mess. At the time the game versions of the cards couldn't use overlay planes in Open GL, which Maya uses.
The Quadro cards could do all of this. I would definitely recommend you get a Quadro card for Maya. I use a K2000 now, which is a bout $400ish, but a K600 or K620 are really pretty cheap at about $150, and do pretty well!
It's not just about speed... but the Quadro cars kill the game versions in Maya..
http://www.tomshardware.com/reviews/radeon-r9-290x-hawaii-review,3650-33.html
I just looked up the current version of Maya, and they said this about using a DirectX11 card like a GTX with Maya. basically the GTX type card is very slow at OpenGL, and if you use their Viewport2.0 to render in DirectX 11, then you won't be able to use these features...
The following features are not supported in Viewport 2.0, and do not function with HLSL shaders when using the DirectX rendering engine.
Hair
Fur
Fluids
nMesh (cloth)
Particles
Paint effects
Hierarchical subdivision surfaces
Active stereoscopic cameras
Light linking