Depends on "ideal." 75 mph will suck range down pretty quickly — much faster than 65 mph, for example. However, nav will make the initial estimate of battery percentage while charging based on usual and customary speeds for the route. It isn't always accurate so be sure to add in a sizeable buffer until you get used to how it compares to your driving. Takes a few trip legs to get a feel for it.
Nevertheless, once you get going and Nav sees your actual energy consumption, it will adjust by shifting the estimated percentage at destination. If that number is dropping steadily, rather than dropping then stabilizing, slow down a bit until it does stabilize. Or pick a nearer Supercharger Station and blast away. Even five mph makes a significant difference.
Most road trip newcomers will charge to a higher buffer to get comfortable what the real range is on a given highway at speed. Do be aware that rain or headwinds can decrease range by a lot — if you face such weather, charge a bit extra. I consider 15% plenty for a typical road trip leg but you might want to go with 20% to 30% at first.
In general, shorter trip legs, say 100 miles, have a lot more leeway than longer ones over 200 miles. There is less time/distance to use up the buffer on short trip legs. In my Y LR I routinely do 150 to 200 miles, but any longer than that and my partner and I will need a restroom break anyway. More short charges are easier to manage than a few long ones. Four and a half hours is my typical driving limit without a rest stop and that's pushing it. Three to three and a half hours is better. YMMV.