This has been covered in other threads pretty well. The numbers suggest that there are only two rules that make a big difference in overall cross country speed when using Superchargers:
1) Drive as fast as conditions allow between Superchargers.
2) Arrive at the next Supercharger with the minimum SOC possible, to maximize charge rate for as long as possible before the charge ramp algorithm lowers the rate.
The speed you drive while trying to follow rule #1 is a personal choice (optimum speed is much faster than any real-world speed limit you will encounter); so too is the 'minimum SOC' you'll feel comfortable with in #2. But if you're a law-abiding citizen and tend to drive the speed limit, or near to it, you'll be so far below the optimum speed that only rule #2 has any meaning.
From my years as a competition glider pilot, I know that choosing a slightly lower-than-optimum speed to fly is not very costly in terms of overall cross-country speed in classical thermal soaring theory (which is almost perfectly analogous to driving an EV cross-country).
One factor that you can't control for is how much overhead each charging stop costs you in terms of time and distance spent not making progress toward the goal while accessing the charger, and then returning to your route after the charging stop. As that overhead increases (accessing the Glenwood Springs Supercharger incurs a huge penalty; Blanding, OTOH, is right next to the highway), optimum speed-to-drive drops a fair bit, but is still well above the legal speed limits you'll encounter on the highway.
I just finished a 2400-mile, mixed Supercharger/L2 cross-country trip. In practice, if I'm headed from a Supercharger to another Supercharger, I charge only to a Rated range that gives me a comfortable margin under the expected conditions (I aim for about 30 miles of cushion, but on this trip I arrived at Superchargers with anything from 27 to 60 miles of Rated range remaining: you may be less conservative than I, but I'd rather be comfortable than anxious); if I'm going from a Supercharger to an L2, I stay until the actual charge rate at the Supercharger falls below the expected charge rate at the next stop, measured in kW.
One other consideration: if you have an 85kWh battery and the Superchargers are spaced close enough together, it can actually improve your overall speed to bypass a Supercharger in order to both avoid the charger access overhead and to arrive at a lower SOC at the next Supercharger, even if you have to drop your travel speed somewhat to make it to the next Supercharger. Glider pilots also have this rule of thumb: everything else being equal, the fewer times you stop to climb (charge), the faster your overall speed-made-good will be. What glider pilots can do that Teslas cannot is to 'charge' (climb) while underway. But that's a whole different subject...
