Ok - managed to add a new fuel up from this tank - forgot the SG2 was linked up and records tank miles - 732. So updated that.
The end of that "tank" was a 400 mile round trip today. I did an experiment and set the cruise at 70 (UK motorway limit) and was of course passed by everyone. At the far end of the journey I got this on the OBD :
It did go over 41 on the way back but I didn't get a pic.
That is cruise alone, no hypermiling. OBD displayed 39.7 at the end of the trip including the last 40 miles being "spirited" driving on the A701
EDIT - for info this tank was split into 2 parts as I wanted as empty a tank as I could manage for a supermarket fuel discount (6p a litre) due this weekend. I got my £4.odd.