To get the best picture quality and best viewing experience from a 55 inch Television you should sit at least 9 feet away from the 55 inch Television.
Sitting any closer than 9 feet from the 55 inch Television will give you a worse viewing experience and even eye strain in some cases.
I have a 55 inch TV and I had it in another place in my living room and had it 7 feet away from my couch and the picture quality and viewing experience was poor until I moved it to another part of the living room and 9 feet away from my couch and the viewing experience on the 55 inch TV is much better.