How much should the dialogue(/narration) in historical fiction be 'Austen-esque'?

I'm debating giving my novel a historical setting (probably either 1700s or 1900s, since there are events in both that tie in very nicely with the plot).

The problem is I'm intimidated by the dialogue(/narration) aspect. I have no idea how to write historical speech. Dialogue is a weak point of mine anyway, add in making it feel believable and not forced in a historical context and I'm completely lost. I've also read more classical fiction than modern written historical fiction so I'm not sure how good a representation that is of the expectations of historical fiction written by and for modern people.

Does anyone have any advice on what to look for when writing this kind of dialogue, how to know if you've taken it too far, how far isn't far enough?

(Also, if anyone has any recommendations for entry points into this genre that are good examples of the kind of dialogue expected in this genre, it would be greatly appreciated!)