Assuming both guitars are constructed exactly the same, in terms of tonal characteristics what would be the difference between a grand auditorium and orchestra model shape and what styles are these shapes usually associated with?
as i understand it, the GA bodystyle is a general all-around shape that takes well to a little of everything. good for fingerstyle and strumming. the GO style does fingerstyle well but really shines as a strummer. it usually has a big booming voice compared to the more precise notes that a GA makes. i know it's a bit more complicated than that but, in layman's terms that'
ll work.

i have 2 GA style Taylors and they both play very well. i cant use the larger GO( or jumbo if you will) size as i have a shrapnel( or bullet, not really sure) wound on my right shoulder that makes playing a larger guitar extremely difficult. i would love to play the larger voiced GO's but oh well....
Those terms really have no exact dimensional definition, so I can't give you an absolute answer. It would just depend on the particular manufacturers size specifications. The manufacturer of my guitar calls it a "Grand Concert", but it's only 3.5" thick at the neck, whereas most other GC's run about 4" - 4.25", and are rather awkward for me to play.

It should also be noted that there is always some variation in guitars just due to random factors. My advice is to get the box that you feel most comfortable playing... assuming it sounds OK, then the really important factor is your own personal skill.