I have a .8 gain Draper grey screen, and while I am very happy with it, I would rather have the punch of a 1.4 gain screen than a grey screen hands down. The NON-positive gain characteristic of this grey screen keeps viewing angle wide and completely eliminates any hot-spotting at all as far as I have seen.
It is typically the positive gain - especially high power screens, which cause hot spotting and often have very narrow viewing angles.
At the end of the day, I would not put a strong recommendation on a negative gain grey screen, but I think you would have best results with a positive gain grey screen from a good manufacturer, including Dalite, Draper, or Stewart.
Yet, at the end of the day, I typically recommend a Carada brilliant white screen unless the conditions just don't allow for it.