Was that at 90 km/hr or 120 km/hr? I think not. So what you get in traffic is of little consequence to me and most riders that buy a BMW for long distance touring...usually above 100 km/hr. When I buy a bike, the first two things I look at are fuel quantity and fuel consumption...because we all know what pitifull range 90% of motorcycles have. In any case, you had one very bad R1150 GS and have one very good R1200 GS. I guess I'm lucky with my Adventure seeing as I get in the mid 300s on 30 liters of gas at a good clip.
It doesn't matter a jot what speed it was at, it was the consumption that I recorded in the conditions that I encountered on my regular commute to work. As for suggesting my 1150 was "bad", the figures I was obtaining in London traffic conditions compare with a number of other 1150 owners who find themselves commuting in similar conditions. In fact there are others out there with 1150's who were recording less than 40mpg in similar conditions.
Yup, 3 liters larger for a whole 9 extra miles at the published speed of 120 km/hr. The new Adventure takes a nose dive in fuel efficiency compared to the regular GS...lots of drag. And so that we don't ping pong further...like I've always said, you R1200 GS has better numbers based on what I believe, the BMW published claims. You might do better or worse (obviously) depending on your riding style. Too bad they keep reducing the fuel tank size for an overall shorter range. My friend wished his R1150 GS had the 25 liter tank of the previous model...so do many owners.
I think you'll find the 1200 Adventure will go a lot further than 9 miles more than the 1150 predecessor. That is the experience of owners who have them. Perhaps when you go out and buy a 1200 Adventure, put the miles on it and then get your own figures you'll be in a stronger position to comment, but right now, your experience of the 1200 is zero, so it doesn't really give you a strong platform to compare. I think I will listen to the 1200 Adventure owners who report that the fuel consumption on their new bikes is superior to their old 1150. They are in a much better position than you to relate their experiences.