I see many cedar baskets in 10,12,14 inch size on internet.You may want to consider those. For example this one-
ORCHID BASKETS
That will eliminate all the worry about overpotting and media since you can easily keep chunkier media and baskets provide enough air.And they will be stable.
I grow cattleyas in both, clay pots and baskets. Roots like ample space baskets provide though clay pots look better. Baskets are lighter than clay pots.And easier to hang because of hooks on them(if you decide to hang it).
Also, don't you think it is better to divide in spring/summer when plants grow roots/leads faster ?
And you may get away with 2 or more smaller pots instead of one huge pot at that time.
Because plant will probably keep traveling in one direction and you will have same dilemma sooner or later, you may want to consider dividing by making a cut in the rhizome (leaving at least 4 p bulbs on each division)while plant is in the same basket( in spring, without disturbing any other part). In time you can separate them after they grow leads and put in smaller baskets.
Just my
![Two Cents](http://www.orchidboard.com/community/images/smilies/twocents.gif)
I bought some large Cattleyas from Hauserman recently, may have to use my own advise.
![Rolling Eyes](http://www.orchidboard.com/community/images/smilies/icon_rolleyes.gif)
![Scratch chin](http://www.orchidboard.com/community/images/smilies/new/scratchchin.gif)