If your room is 5.5m long, the largest screen size will be about 113" wide.
Our dem room is a similar length and we have a 104" wide 16:9 fixed screen and that is a very comfortable size image.
I personally wouldn't go beyond 9 feet wide in your room.
I sold a 300 to a countryman of yours called Edward Spiteri.
If I can find his address etc I will let you have it.