Distance/Screen SIze Formula?

My husband and I are debating between a 50" and a 60" flat panel television for our living room. Although the room is very long , it is not very wide and we would be veiwing the televsion from aprox.12 feet from the screen. Does 60" seem like too large a screen for that distance or can we go for it?We hate the feeling of sitting in the first few rows of a movie theatre.........hence our concern. Can anyone help?