I bought some 1.2 gain matt white material to make a 100" fixed screen. It came from Ellie, http://www.ellie.co.uk , and works very well on my AE500. You can buy ready made fixed, manual and electric screens from them too.
At the screen size you suggest you may find that the blacks look a bit on the grey side even with the lamp brightness set to low (I did). If this is not to your taste you may want to look into a grey screen. I've heard these help with black levels. More information at https://secure.room2.co.uk/harknesshall/