We have reservations for the first two-three days in San Quirico d'Orica and the last night in Siena. Any thoughts about the 1-2 nights in the middle? We are renting a car in Siena.

You want a place to stay between San Quirico and Siena? They're only about an hour apart. I don't think it's worth packing up and moving to a new location between the two towns. Any particular reason you want a third location?

> Any thoughts about the 1-2 nights in the middle? <
I agree with adrienne.
But if you must: San Gimignano

Bolsena and/or Orvieto.

Day 1: S.Quirico - Pienza - Montepulciano - S.Quirico 50 km.(night in S.Quirico)
Day 2: S.Quirico - via Cassia (with diversion to S.Casciano dei Bagni, if you enjoy thermal baths) - Bolsena 90 km. (night in Bolsena)
Day 3: Bolsena - Civita di Bagnoregio - Orvieto 40 km. (night in Orvieto or back to Bolsena)
Day 4: Orvieto - Siena 125 km.(night in Siena)
Day 5: Siena - S.Gimignano - Volterra - Siena 130 km. (night in Siena)

Average drive 60 km / hour

Ohhhhh...after reading about the Orvieto suggestion and thinking that Orvieto is not in the middle between Siena and San Quirico I suddenly realized that the OP was probably asking for where else to stay the other nights, not asking for a location in the middle between Siena and San Quirico. Now it makes more sense.

I loved staying in Orvieto!

Thanks for all the help!