Went 2.5k round trip last summer. Its not too bad, and I have "old guys back" pain. You will be stoping for gas every few hours anyway. I got some of that soft foam block, and cut some wedge shaped pieces and put under the seat cover for lumbar support. and that helps. Have fun

 

I pratically live in my S

 

9 hr is drive is fine to do with S.
i did several road trip in my s, and usually do about 15 hr stright drive when on the way back except fuel and bathroom stops.

I usually carry warm hat and jacket in winter season so i still can drop top.
Just don't forget to bring a small blanket to cover your knees which will make it so comfy in a long drive and pillow to take a nap in pit stop.
It's total PITA to take a nap in S without those 2.

 

My only problem with long road trips in the S is, if I have a passenger there is a lack of room for beef jerky and gummy bears .....

But as far as comfort ... I prefer it over my expedition....