This is a tough one. There is no ideal staffing rate really, since the difficulty and strategic importance of the project are crucial parameters in the staffing process. At BCG, we could overstaff a project that is very critical to us, in order to position ourselves better for future work. Similarly, we could understaff a project that we know is within our realm of expertise and would allow us to knock the ball out of the park without much effort.
Hope that makes sense!