The cards' hardware is pretty much the same; they can deviate in BIOS versions, and as said previously, Quadro's drivers have been licenced to work in CAD environments.
For home use, both cards support the same funcionalities, and there's hardly a difference in their OpenGL support (some OpenGL functionalities, specific to CAD, are disabled in 'mainstream' drivers - they are of no use in games).
You can get a 7900 GTX card, patch its BIOS, find leaked and patched Quadro drivers and have yourself a professional grade system for 1/4th of the price - but with absolutely no support and a cancelled warranty.