I've hesitated a little in responding... I don't feel like being a restaurant critic, at least not publically...
But you deserve an honest answer, so here we go...
Firstly, I have never been to the restaurant at San Donato. If you go, please get back to me here on the forum and tell us about it.
For the other ones mentioned... Generally, I feel like I'm too discriminating towards restaurants since I had one myself. I either love them or not.
In any case, I feel confident in recommending Butcher Dario's places in Panzano - they are worth the experience!
My second favourite in the area is "A Casa Mia" but however, it's a good windy ride from Radda and perhaps too far away.
Lamole isn't bad at all even though I find it a slight bit pricey... - perhaps the view (and the tourists that the view has attracted) has been added to the price list?? Others would probably argue that the Chianti region as such is famous and therefore is entitled to particular treatment...
I don't really feel like commenting on the kitchen of the Bottega in Volpaia. I know the owner Carla rather well and she's a great person who's backed up by her sister Paola (BarUcci) and her mum Mamma Gina (featured in the book Too Much Tuscan Sun)
I haven't eaten there in over a year so I can't give you a recent feed-back, but - quite honestly - the thing that really annoyed me when eating there was that the menu NEVER changed with the seasons - as it should according to available foods (which is expected of a good country restaurant in Tuscany). In fact, I was never impressed by the food and had negative feed-back from certain clients also. However, the setting is absolutely enchanting and, in fact, the town is definitely worth a visit!
As mentioned before, I would love to hear from you when you get back with your experiences and preferences. It might enlighten myself and help other travellers also!