I still have an O27 figure-8 layout on a 30"x 79" door and I still have fun with it. A figure-8 is more interesting than an oval IMO, plus it keeps most of the track away from the table edges. The crossing in the center creates an interesting feature which can be imagined as two different railroads. My O27 end curves have O54 'easements' for improved appearance and operation. I custom-built a 67-degree crossing to make it fit the space. A similar arrangement could be done with O31 in slightly more space.
I have some ideas to improve on this with minimal additional space.
