Yeah, I agree with Andrew's numbers, 14'10"x19'. When I was looking for a rental house with a garage, I came up with the same numbers as the minimum garage size that I'd go for.
However, if I already had a place to live and was looking for a table, I'd still go for the 9' if my space was 14'x18'. My reasoning is that you will only need the extra 5" for a very very small percentage of shots.
The cue ball needs to be on or very near the rail, AND you'd have to be shooting the cue ball at a 90 degree angle out from the rail. In those cases, you'd have a 1" back swing with a 58" cue. So, personally, I'd probably buy an extra 56" cue (or cut some house cues to 54", 55", and 56") to allow a 3" - 5" back swing for that very small percentage of shots.
Not ideal, but worth the sacrifice in order to have a 9', IMO. I could understand how some would feel that it wouldn't be worth it though.