I suspect sustained operation over time is more important for trucking than sheer speed. That's why robotics are so interesting to trucking firms, because robots don't sleep, stop at truck stops, hit up hookers at rest areas, whatever. They just keep on...trucking. So a robot truck that goes 24/7 through the night at the speed limit or even below is still a lot more efficient than a human-operated rig. Going faster adds complications that might not be worth it I am guessing.
On the topic of Musk, though, I'm deeply suspicious. Yes, he has a history with fast cars, and yes, the Teslas are wicked fast. But to me they are less cars than, well, rolling cell phones. Musk's attitude seems to be that cars qua cars are dead, and we should be thinking of transportation like this the same way we think about iPhones, and consume them pretty much the same way. He's building a walled garden ecosystem a la Apple, and the cars themselves are aggressively eschewing many of the traditional trappings of cars, especially in the interior.
He makes fast things for engineers and people who think like engineers--focus on the numbers, and get bedazzled. If you're into speed, and nothing else, I can see how these things inspire. They leave me totally cold though in ways that much slower ICE cars do not. YMMV.
