The screen choice has more to do with your room conditions than 3D or gaming. If you watch with very little ambient light hitting the screen and your room is dark (ie. walls, ceiling) the white screen is a better choice. If you have light hitting your screen and/or your screen is close to white or light colored walls or ceiling the gray screen would be a better choice. You do lose a little brightness with the gray screen but I don't think it will be a huge issue on your screen size unless you are trying to overcome a fair amount of ambient light.
If your projector uses a passive 3D system (which the 6010 doesn't) than you would want a screen that holds polarization, neither of the Dragonfly screens hold polarization but it is not necessary for your situation.