I plan to build in this room a layout of 5' 8' because that's all the room I have to do so. Why not 4' x 8' I would like to have more than one loop and need minimum of O42 for some of my engines. So I will go with O54 to help the over hang somewhat . 4' x 8' I believe is the start of every great railroad empire.
Mine has an outer loop with 042 curves, no switches or uncoupling tracks. That allows me to run absolutely anything on it.
The inner loop has standard "O" gauge curves, with switches and uncoupling tracks.