I put my wallet in the storage bin and use a small pillow to support my back when driving. Made it from GA to MI and back this spring with no pain!
I DO have leg pain at times from sitting in the car, van or truck and from sitting at work. Started seeing a chriopracter 3 weeks ago and I'm almost pain free!
So, support that back and you should be fine - oh, and I started seeing a chriopracter as early as age 26 - so I AM one who can have pain, but the XF is still a good and fun car for me to drive.