40 miles from Palmdale puts you at the bottom of the 14 Freeway, 60 miles away is Downtown, correct? Haven't tried it yet.
Here's a data point you might consider: I live in Santa Clarita (elevation about 1200ft); going back home from anywhere in the LA Basin that's 40 miles away takes me about 60% charge (~11kWh), if I drive at freeway speed limits. Knowing that, I don't think I'd venture to Palmdale for the first time with anything less than a full charge from the start of the 14 freeway. I would also favor taking Sierra Highway instead of the freeway; easier to hypermile without pissing too many people off due to its lower speed limits.
If starting 60 miles from Palmdale, I'd top off at the free Sylmar Metrolink charger before starting the ascent.
Let me know if you try it... I'll post if I end up doing it.