I just did a 900 mile road trip last weekend, Denver to Albuquerque.
I used evtripplanner.com (which was very close to real-world) and I would just change the speed from 1.0 to 1.05, etc. and look at total trip time. Since it takes into account charging time it worked out that 1.15 was about 6 minutes quicker than 1.0. That equated to 84 mph. That would have me arrive at each charging stop with about 25-30 range miles remaining.
BTW- the most boring Supercharger on the trip... Las Vegas, NM! Nothing there!