Thank you all! The F-Stop ICU look pretty good!
I am rather tall (only a few cm shy of 2m) so finding a fitting backpack is not that easy - I usually carry around a 38l Deuter trekking backpack in longer version - I don't remember the name of the pack - but it is very comfortable for my long back. I think the medium or even the large ICU would fit perfectly!

(With larger backpacks it get's a bit easier - for my 8x10 my wife sew a simple "case" that I can put in a 60/70 litre front loading backpack, add couple of holders, a lens or two, the meter, loupe and all in the top pocket and go.. but not that far, obviously )