ilw-00
I, too, have X and 9.2 on separate Pismo partitions (with docs on a 3d - to ease back-ups). I can see no reason why you couldn't put docs anywhere you find it to be convenient.
My experience has been that operations "across boundaries" are smooth and, essentially, seamless. Open a doc and the appropriate app is available.
I did something - - for the first time last week - - by installing on those separate partitions the respective X and 9.2 drivers required by Canon's new portable printer . Both, it seems are needed, depending upon the particular application used in printing. Selection was, also, seamless.