If I understand correctly, this can be done in the shell using less than 20 characters (yeah, shell!):

    sort -u Sub*/*html
[download]

With the added benefit that sort knows how to sort huge lists efficiently. (This is assuming that your shell doesn't have problems with the number of arguments that result from the expansion - but even then, a shell solution is way smaller)

But if you really want to save time, you shouldn't look in sorting/uniquing phase. Look at the updating phase. Keep files sorted. Reduce the number of files. Reduce the number of files per directory.

Abigail