Yep. For further curiosity, I did a count on how many substr calls there were. For the ST, of course, you have two for each element, one to get the first 8 chars and one to get the rest. So for a million-element array, that's 2M calls. But for the sort-on-substr version, I got about 37M substr calls. That'll vary some depending on how unsorted the original array is, but that's probably a good ballpark number.
That's a lot more substr calls, but I guess it's still less work than building an entire new million-element array (with each element a reference to a two-element array), as the ST requires.
It does give me a (very rough) rule of thumb, though: for the ST to be more efficient, the alternative probably needs to do the equivalent of 8-10 substr calls. So just a few core functions probably won't qualify, but a longer series of functions, or some fairly complex regexes, or certainly any sort of file or database lookups, probably will. And there's always measurement to see for sure.
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