Thanks again for all of your advice, a lot of it was VERY helpful (and calming

) I will respond to some of your questions/comments individually a bit later...In the meantime, I just wanted to share the raw data from the various legs of my trip, as well as some conclusions...
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Vehicle: Tesla Model S P85 w/21” wheels
Passengers: 2 Adults, 2 Kids (450lbs)
Cargo: Luggage for 1 week (200 lbs)
Exterior Temps: Start: 45 degrees, falling to 35 degrees
NYC --> Philadelphia, PA
ACTUAL MILES: 108
RANGE USED: 138
RANGE LOST: 30 miles
LOSS PERCENTAGE: 28%
ENERGY USED: 44.4 kWh
AVERAGE: 386 Wh/mi
NOTES: Normal highway driving (55-65mph, no cruise control), normal heat usage (68-70 degrees), lite/no traffic.
Philadelphia, PA --> Newark, DE
ACTUAL MILES: 37
RANGE USED: 48
RANGE LOST: 11 miles
LOSS PERCENTAGE: 30%
ENERGY USED: 15.5 kWh
AVERAGE: 397 Wh/mi
NOTES: Normal highway driving (55-65mph, no cruise control), normal heat usage (68-70 degrees), lite/no traffic.
Newark, DE --> Glen Allen, VA
ACTUAL MILES: 208
RANGE USED: 214
RANGE LOST: 6 miles
LOSS PERCENTAGE: 3%
ENERGY USED: 62.5 kWh
AVERAGE: 301 Wh/mi
NOTES: Cruise control 55mph (when able), minimal/intermittent defogger usage, moderate/heavy traffic, very flat route.
Glen Allen, VA --> White Sulphur Springs, WV
ACTUAL MILES: 193
RANGE USED: 224
RANGE LOST: 31 miles
LOSS PERCENTAGE: 16%
ENERGY USED: 65.3 kWh
AVERAGE: 339 Wh/mi
NOTES: Cruise control 50-60mph, minimal/intermittent defogger usage, lite/no traffic, mountainous route
CONCLUSIONS:
> The combination of not using cruise control and using consistent heat led to big losses in rated range (although I can’t say which contributed more/less).
> Using cruise control with moderate speed and limited heat/defogger use on a flat route was very efficient…Even with heavy payload/cargo, came very close to 1:1 mileage.
> 1.5 hours of stop-and-go traffic in the middle of the Newark, DE – Glen Allen, VA leg didn’t seem to have significant effect (50-mile breakdowns were almost exactly consistent).
> Defogger conservation was problematic: On low fan speed, it would just blow out cold air, even if the temp was set to high. We ended up turning it on sparingly when needed.
> In extreme conditions (cold weather, heavy payload/cargo, routes with elevation), calculate for a 20-30% loss of rated range at minimum!
> We had several backup charger locations (Via ChargePoint, PlugShare, KOA/Campsite apps), and had address/phone number/directions written down (in case of no cell signal).
> While we did restrict our speed somewhat, and used heating/defogger sparingly, thankfully we never had to radically slow down or use an interim/emergency charging location!
> The energy/rated range consumption estimates from EVTripPlanner.com were way too conservative, to the point where it was unusable. Even when I low-balled my figures, their estimates were way off-base from reality. On one hand, it made me super-prepared, and hyper-vigilant about my energy consumption...On the other hand, it led to range anxiety, and created a lack of confidence in being able to use it as a viable tool for EV route planning/energy consumption.