I've got a E39 M5 and have read that you should be able to get 70 l into the tank but I only seem to be able to squeeze about 60 litres into it - do you know if M5's had different sized tanks or maybe I've got some issue going on here?
I rarely got much over 60 litres in my old one, but then I didn't tend to run it low. In the grand scheme of things to worry about, this wouldn't even register.
I had an M5 reading 3 miles left in the tank (drove it home from the Nurburgring to Woking on one tank) and then put 72 litres in it. Clearly some of that was in the filler neck.