I drive for a living. Occasionally I'll do a 400+ mile day. Those are brutal.
Discussion
Today's total was definitely over 400. I just happened to do 310 without stopping.
My longest is still 16 hours straight through to Wyoming, followed by a 3-hour nap, then 9 hours to Vegas. That was rough, but I could (and would) do it again if I needed to. I've driven for a living (as a courier) before too, but that was a long time ago.