Do you really have to worry about overdressing? Personally, it never makes me feel uncomfortable to be the best-dressed couple in a restaurant, particularly if I'm celebrating something.

If you're more concerned about other diners' casual dress detracting from the special experience, that's a different matter. In that case I think you're going to want to kick things up a notch from the restaurants you listed and consider places like Joel Roubichon, Le Cirque, and Aureole.