Not to beat a dead horse, but hope the frame-spacing info is helpful to
some of the bee crowd out there.
 
Here's my final offering on this, an instance of 9-frames being problematic:
 
I once had a friend who got interested in the hobby, and got a half dozen
hives or so, all new equipment.  This was back when we were in high school
(early 80's).  Well, as often happens, we got involved with other things (&
a different sort of females) and the bees were neglected for 2-3 years.
Then we decided to check them out one day.
 
He had used 9 frames in the brood boxes.  What a mess. In a number of
hives, the combs were all spaced crazy, many of them crooked, others all
coated with gobs of old propolis. Some frames had portions of double-combs
on them, etc. etc. -- it was a lot of work trying to inspect some of those
colonies. The bees didn't appreciate our knocking things around, either!
That was a good example of the improper use of 9 frames, and I'm careful to
not let things get sloppy like that!
 
I was also surprised to see this topic covered quite thoroughly in a
recently-published German beekeeping manual.  Evidently the idea has its
proponents in Europe as well.
 
It's always helpful to discuss things like this with other local
beekeepers, to see what there experiences have been.  There are always
variations between colonies as well.
 
Best wishes to all,
 
JG