I wish more people would ask this question, to me, it is the true mark of experience. In general, I think of PostgreSQL as the leading Relational Database. The farther you get away from relational data and relational queries, the more I would say, you should look for other products or solutions. But if you want to store relational data and then run queries over it, then stick with PostgreSQL.
Where I did this on the TB scale, we had some sort of ranking but it was not based on ts_rank.
On the PB scale systems I work on now, it is distributed, and we don't order in PostgreSQL (or anywhere else, though if someone wants to write to disk and sort, they can do this I guess)