I think it's probably more the need to set retainers northbound, than higher speeds southbound. The mathematics can be summarized like this: You always lose more time stopping than you can make up for by speeding. If you are going 20mph, and you stop for 3 minutes, you lose 1 mile. To regain your schedule, you need to double your speed (40 mph) for an equal time (3 min), and it takes twice the distance (2 miles). If you can only increase your speed by 50% (30 mph), you need 6 minutes and 3 miles to regain schedule.

I looked through the timetables in Jones & Register, and although there are only four examples, I found a couple of intricacies worth pointing out:

- In 1910, the southbound timings (in minutes) are 8, 10, 7, while the northbound timings are 7, 12, 8. Depending on which trains you pair up, you can make NB equal to or even faster than SB.

- The caption on p.354 makes the following assertion: "...the differences in the schedules undoubtedly were based on the amount of work each mixed train normally was expected to do."

- Alna Center is a flag stop, so the timing is going to be squidgy at that point anyway. I wonder what happens when you look at timings from SS to Head Tide.