Don't worry about it. You have Cordes Lakes as insurance.
Keep an eye on the Energy:trip screen. if the predicted energy remaining the battery at the destination is at, or heading towards, an uncomfortable level, stop in Cordes for 5-10 minutes, add a reserve and continue on. I bet that you don't need Cordes, but if you do, it is a good, quick safety net.
I did Central Phoenix to Flagstaff last April in a P85 with no problem. I thought I would have to stop in Cordes Lakes after going 65-70 MPH up the long hill. When I got close to Cordes, it was obvious that I could keep on going to Flagstaff with energy to spare.
I have a 60 and did North Scottsdale to Flagstaff in winter (albeit a warm day -- never dropped below freezing) before Cordes Junction was avail. Arrived with 13 RM left (and drove the speed limit all for the last 20 miles)… Was passed by an S85 on the way too (it was charging at the Supercharger when we arrived)...
Thanks to yesterday's price reductions, I upgraded my 60 to a 75 and ended up pulling up this old thread. Interesting thing I noticed while playing with evtripplanner. It says an S85 will take 200RM from Scottsdale to Flagstaff, which is what was confirmed earlier on this thread. It says the S75 will do this in 173RM.. not sure I buy that, but interesting.