When you see all three together, you get a real sense of the relative sizes of each. Some trains on the branch must take a leisurely pace as neither 6 nor 7 look like they achieve a high top speed. Also, based on the size of the "regular" fleet, does it mean no. 9 and no. 10 are the largest locos the branch can safely take? Certainly wouldn't get no. 4 up there.