If it'll help, I just did Northridge to Carson (CSUDH) and back (82 miles). Cruise control @ 55 as much as possible, a bit of traffic on the way back (which may have helped!), about 1200' of elevation drop to Carson, and the same back up to Northridge. No climate control, ~50-70°F, made it home with 4 miles left (whew!).
So I'd say set the cruise to 60 and you should be fine...
OT: garygid: What have you found the availability of the Mitsubishi QC unit to be?