The GOM is exactly that, a guess. I routinely exceed the initially presented range, especially if I do any amount of freeway driving.
If you change the dash view to the consumption gauge (the one that reads from reset), and reset that gauge, the range should change to 83 miles. With careful driving you can likely exceed that. If you do a lot of stop and go, then you might not achieve quite that much.
I've had times when I've done a full (non-range) charge, and around 60 miles were indicated on the GOM. Then, after a 16 mile drive to the dealer (to get a free carwash), the range has only gone down 6 miles, instead of 16. The more you drive, the more it tends to give a more accurate estimate.
I rely instead on the state of charge (percent) gauge. I keep track of how many miles driven since last charge (using the trip meter), and using the miles traveled, and percent of charge used, I get a more accurate view (I believe) of how far I will be able to travel.