Length is calculated by a formula.
3j was always deliberately vague on exactly what was taken into account when calculating story lengths.
About seven months ago, the formula was reworked to make it much harder to achieve 8/8. See italicized notes from the update below:
So, length calculations have changed to provide higher resolution in the higher ratings. Now, a 5 is a decently long game, a 6 is a long game, a 7 is a VERY VERY long game and an 8 is extremely long. There are only 9 length 8 games now.
If two storygames have the same lengths in a category, there's no tiebreaker. It's just random which one is higher.
The way lengths are calculated has changed AND in general, lengths have been decreased. There are many more storygames rated 4 and 3 than before. What hasn't changed is that if two storygames have the same rating, they are the same length. The one that is higher up in the category when you sort by length, is random. If you sort by rating and then sort by length, the one with the higher rating will be higher, if you sort by name and then by length, the one with the earlier alphabetical name will be first.
The Nine Games with 8/8 Length
Dead Man Walking (so far higher than the second longest story, it's not even a little funny)
Eternal
Ground Zero
MyVacation
3 of the Homo Perfecti
Dungeon Stompage
A Game of Life and Death