Hi, I am about to buy a PJ and I need to find a good screen. I understand that gain has to do with the ambient light present in the room. However, what I do not understand is knowing which gain you need for certain rooms. If someone can please explain to me to figure out which gain I need for my room, that would be great! BTW: I have Greyish / White walls and the room is 16' x 14' wide Thanks in advance!