I have noticed a curious effect, whereby acoustic treatment "appears" to become less necessary when other quality aspects approach perfection. It has been a great surprise to me, and I'll be quite interested to hear what happens when I do finally try some treatment in the room.
Hi Mark,
So do you perceive your listening room as either bright or dull? Or somewhere in between, Goldilocks porridge style?
It appears your listening room is rectangular & you have the speakers set up along the long wall. I've experimented with speaker placement & have found this arrangement really opens up & in effect dials in the sweet spot, assuming one is far enough back from the speakers. As regards room treatments I have a few sound baffles set up around the speakers to dampen the highs which tend to ricochet all over owing to the brightness that a hard floor, peaked wood ceiling, irregular angles & glass doors / windows enhance. They help but do not cure the problem of excessive brightness. I do notice that they contribute to focusing the sound, so that is a plus, at least as regards my particular situation. The room is simply too big to effectively treat without going to extremes of room partitions, wall to wall carpeting (on the walls!) & drop ceiling panels.
I'd venture that your room is close to an inverse of the golden ratio (3/2) that Winston Ma espouses.
www.positive-feedback.com/Issue3/maroom.htm
A funny thing is that John Dunlavy proposed the exact opposite, the so-called "long wall" approach, to optimize the reproduction of his speakers, of which I have a pair of model IV A.
www.audiocircle.com/index.php?topic=69766.0
www.audioasylum.com/scripts/d.pl?audio/faq/audiophysic.html
www.stereophile.com/interviews/163/index.html
Responses from 2/24/10 onward in the below linked post address speaker placement & sound baffle considerations.
forum.audiogon.com/cgi-bin/fr.pl?cspkr&1266960928&openfrom&1&4#1
My thinking is that the characteristic of the room itself, in regards to the materials used to finish it (wood, plaster, carpeting, glass, etc... ) and how that will effect the relative brightness or flatness is as important a consideration as the general spatial dimensions, though of course they work in concord in regards to coloring / effecting the sound generated from a pair of speakers.

