I'm also planning to go to Calistoga with a rented (!!) model S 85kWh from SFO airport - and I have a few questions...
(1) Route: Google Maps tells me I should go through Napa but last time I took this route, long non-highway roads and took a long time. Isn't it faster to take Highway 101 north up to Mark West Springs Road and go east from there? Looks like a little bit mountaineous road though.
(2) Charge: I think it is approx 90 miles one way so if I slow charge somewhere in Calistoga and don't drive around too much there, I can get back to Fremont Supercharger (Calistoga - Fremont 100 miles)? What do you think? I will ask Hertz to range charge just in case but I'm not sure they can correctly do that...