There is a rating higher than 5 stars, called TOWER. It has been a while but if I recall it is very difficult to reach that with offices, because they have a large amount of traffic compared to other ways of getting population, making it to hard to not overload your elevators even with optimization.

What I did was sort of a hack, but worked, in the basement levels express elevators and escalators can go to any floor, so I made tons of them, and made tons of shops, all shops (they had highest population density). Virtually all of my tower was underground.