I have also had 46mpg over an 80 mile drive through the welsh mountain roads and shropshire roads just keeping up with the usual traffic and having a bit of fun whenever I got the space ahead of me.
What have you achieved with what engines?

In my humble experience the discrepancy of indicated to actual is or can be way more than 10%. I am currently averaging around 43-44mpg actual on a tank to tank basis. I must however say that most of my journeys are less than 30 miles, and a mix of A road and a little town work. This is with a 180D R sport.