I think it also depends on what course the pasta is being served at. If truly a primi (after an antipasto), then 2 oz. per person is good. Leaves room for a secondi.
If it (the pasta) is a main course, I make 8 oz. Depending on sauce, there may be a decent amount left over, or barely any. But, you gotta have a green or something along with it.
Cooking for two in my above examples.