I don't think the grey/black are superior to white in general. They have more resistance to ambient light. The grey screens are designed to reflect light that is directed straight at the screen (i.e. straight line from the projector), but do not reflect light coming from the sides (i.e. reflections off the side walls). So, if you are concerned about ambient light, choose the grey.
In your situation, with some concerns about ambient light, I would go with the Greyhawk from Stewart Filmscreen. It has a very wide viewing angle (almost as wide as my Studiotek 130), but less gain. The Stewart Greyhawk is more expensive, but it has 12% more gain than the grey screens from Draper and Da-Lite. When using grey screens, I would try to squeeze out as much light output as possible.
I use a Sony VW95ES (which, in my opinion, was the last excellent 1080p projector Sony made) that outputs 1000 lumens. I have a 7-2/3 foot wide screen (92") in a completely dark room and the 1000 lumens is just enough to give good light output once calibration from Lumagen Radiance is completed. In you room, I would recommend at least 2000 lumens (or as much as you could get) because of the larger screen and lower gain Greyhawk. A 10-11 foot screen is really huge for a common project, plus the lower gain screen means you really need a lot of lumens! What's your projector budget?