The average gentry income was 700£ per year.
Therefore, Mr Bennet, who had three times this amount (2000 from his estate + 200 from his wife), was I would say, at the limit between middle and upper gentry. As Sir William and Mr Bennet had visited Mr Bingley, I suppose that both knew, in a way or another, the wealth of these two principal families.
Mr Darcy, with his consequence and connexions, though untitled, was probably moving in "the first circles" as says Sir William, that is, he knows as many people in nobility as in gentry, I suppose.
But in fact at this point, if everybody know he is very rich, nobody know he has connexions in the nobility.