Just imagining the entirety of Google running on 16GB of RAM :).
To answer the question at hand though, MySQL seems great at up scaling with larger hardware, as does Redis (from what I've seen, it seems to almost get more efficient at sizes >500GB). MongoDB (my goto database) occasionally doesn't seem to scale very nicely off the bat, but after some configuration that too scales very well, possibly even better than MySQL.
To answer the question at hand though, MySQL seems great at up scaling with larger hardware, as does Redis (from what I've seen, it seems to almost get more efficient at sizes >500GB). MongoDB (my goto database) occasionally doesn't seem to scale very nicely off the bat, but after some configuration that too scales very well, possibly even better than MySQL.