Yet another vote for 10 here. I had height restrictions so poured a 6" wall and built 8' walls on the footing giving me a ceiling height of 8' 6" which is a huge improvement over 8' (ability to swing a 4x8 sheet of plywood end over end). I would not go for 8. Is the space over the room within the barn any consideration? I would hate to cripple all that potential storage.
Brian
Brian