If you’ve seen this week’s magazine, you’ll have seen, among the plugs for next week’s issue, a trailer for a comparison test between the new Porsche Panamera Diesel and the original, genre-defining diesel sports executive saloon in its latest guise – BMW’s 535d M Sport.

I’m not about to reveal the verdict. What I would like to share with the class, however, is something I learned on the drive out to Germany for the test. Something that I think is genuinely staggering.

It turns out that you can’t set the cruise control on a BMW for any faster than 110mph. UK drivers wouldn’t know that, but you might if you spent a lot of time on derestricted autobahns in Germany. At any rate, trust me: I tried setting the thing for 154mph, and it just wouldn’t let me.

Why? Because I was intrigued to find out how much capacity a 295bhp 535d would have in reserve at the big cruising speeds you can only maintain in the country where it’s made. And there’s an easy way to do that: find a stretch of derestricted road that’s empty and straight enough, get the car up to speed, set the cruise control, reset the fuel economy reader on the trip computer, and watch what happens next. It won’t give you a scientifically accurate figure, sure - but an indication’s interesting enough.