On that route, I always suggest Orvieto--not to be missed.

I would look at this question in reverse. Which route do I want to take to Rome, and which towns along that route would be good for food and atmosphere? When do you want to arrive in Rome, and are you driving into the city?

Since you're talking about dinner, I would think you'd want to travel some distance from Florence before stopping. Artimino is barely outside Florence and not in the direction for Rome. Camaldoli is only an hour or so from Florence and at least 3 hours from Rome. Volterra to Rome is closer to 4 hours, so from Camaldoli or Volterra after dinner you'd be passing through the best scenery in the dark.

For me, it would come down to Cortona, Montepulciano and Pienza from your original list. If you wanted to drop the car before Rome and then take the train into the city, you could add Orvieto and Chiusi to the list (but make sure you know when the rental agency closes). Out of the expanded list, my choices would be Montepulciano (if keeping the car) or Orvieto (if dropping the car).

I would drive due south from Florence through the heart of Chianti (SR222), and after Siena I would continue on secondary roads (SP438, SP451, SP146). The only challenging part is limiting yourselves to just one or two stops along the way, maybe one in Chianti (Castellina?) and a town in the Val d'Orcia (Montalcino, Pienza, San Quirico, Montepulciano) or one of the abbeys if that interests you. I'm biased toward Montepulciano where we spend a week, and we enjoyed our stop at Abbazia di Monte Oliveto which is south of Siena. But all of these southern Tuscany towns have wonderful atmosphere and great dining options. Here's some info on the abbey:

http://www.slowtrav.com/italy/tuscany/monte_oliveto.htm

I do wonder about the timing of the dinner. You are likely not going to finish until well after 8 pm. And if you are planning to have wine, are you then going to continue driving in unfamiliar countryside in the dark? Have you thought this through?

charnees' point about wine is particularly worthy of repeating. Italian laws on blood alcohol levels and the penalties for violations are very strict.

I don;t get this plan. You want to have dinner in a small town between Florence and rome? By the time you're done with dinner it will be 9 pm at the earliest - so you are talking about driving into Rome at 11 pm or later. Also, if you are diving you can't really have wine with dinner (drunk driving laws are very strict - and strongly enforced - even one glass of wine can put you over unless you are a fairly large person.

If you're going to be driving that route I would do it much earlier - and then go for a 9 pm dinner in Rome. No problems with driving into the city late at night or not having any wine with dinner,

I'm not sure why this has anything to do with my question, but if the details help: We are headed for the airport hotel, not Rome which we will be staying the weekbefore therefore we need a place to stretch our legs and eat dinner. Three out of the four people in this trip are able to drive, so for one of us to skip out on wine is not that big of a deal. Personally, I think driving an hour or two in the dark is worth an afternoon in Tuscany over sitting in a hotel our last night in Italy.

What would you suggest regardless of my plans?

Thank you, Jean and BobtheNavigator. I will defintely look into your suggestions!

We ate in several of the small towns between Florence and Rome during a recent trip. I really liked Pienza the best. We ate at several restaurants, but I preferred Trattoria Latte di Luna. It seemed very authentic.

Three out of the four people in this trip are able to drive, so for one of us to skip out on wine is not that big of a deal.

In this case, the 'designated driver' gets an official You-All-Owe-Me-One card.