I am probably the worst person to give advice on this, given you know where I currently am with my situation.
I personally think it is easier sometimes to have difficult conversations in public. I don't remember a time where I have ever seen a couple fight in public. Not saying it doesn't happen but the chance is very small for a "talk" to escalate.
The downside that I see is if the talk doesn't go well then you have the awkward ride home or the evening is cut short. I personally think having the conversation around your anniversary is a good time to talk about it unless you feel there will be strong emotions on both sides tied to that day and reflecting on the past.
Again, I would listen to others with more exp. than I but I did want to give my 2 cents.
M 33 | W 34 | Kids: S4, S3 M: 5/28/05 Bomb: 8/22/09 EA: 8/1/09 | PA 12/26/09 W L: 10/21/09 M L: 11/16/09 | 12/09 to file SA W & Boys Move Out: 3/14/10