Sport seats are by far the best for long trips. I've driven 9hours in one sitting [small stops here and there] and I was super fresh coming out of the car, no aches or pains. The stiff suspension will give you trouble over bad pavement... but if you are on a decent highway you should be fine.
Another issue is temperature.... If you have summer tires [sport suspension stock equipment] and are driving in warm/hot weather [85+deg] then the ride will be downright cushy. But take the summer tires out of their natural happy habitat of warm weather and the ride becomes less pleasant.