On steady speed motorway runs I managed to see 55mpg on many occasions in our X1 (last car) cruising at 70mph. One journey running slower because I didn’t want to get to the other end early, I got over well over 60mpg. I doubt any other petrol car of similar type could beat it. The B48 engine was technologically more advanced and efficient than any other mainstream petrol engine when we got ours and probably still is.
Interesting. I’ve only done half a dozen longer journeys so far and did manage to get 50mpg on those, but you’ve set me a challenge now ?