We were told, when we dined at Moto, that the 5-course and 10-course meals actually presented about the same amount of food -- the courses were just slightly bigger in the 5-course dinner, and, of course, the cost is a little lower. Because of the pacing, 10 courses did not seem overwhelming. However, there were several courses where I would have liked a larger serving, rather than more courses.
I think you're safe any way you go -- and I certainly think 5 courses would be enough to get a feel for Moto's playful magic.