> I am measuring the performance of equivalent cat <file> | sort | uniq -c | sort -n functionality.

It likely won’t matter much here, but invoking cat is unnecessary.

   sort <file> | uniq -c | sort -n

will do the job just fine. GNU’s sort also has a few flags controlling buffer size and parallelism. Those may matter more (see https://www.gnu.org/software/coreutils/manual/html_node/sort...)