My last ten fill-ups have averaged 73.43 mph (bike calculated) / 76.514 (manually calculated). I have the 2016 U.K. model.
Four of those where with premium petrol (Tesco Momentum) which I have noticed does make a justifiable difference for the 5p extra. Though not enough to go out of your way to always get it.
But my riding is mainly getting away from south London for longer rides! Lots of motorway recently too (above included couple visits to the Wye Valley), which brings it down a lot.
I had bike reading of 66.2 mpg on the bike at one recent fill-up (lots of M4 London to Newport), though had 82.0 on another (riding around Suffolk, no dual carriageways, and on Sainsbury's regular).
My best ever reading was 85.1 mg (89.85 manually) after 226.7 miles on Sainsbury's Premium. That was avoiding the motorway from Swindon to Weston-super-Mere via a stop in Bristol, then coming home via Wells, Westbury, and the old A30 to join the A303/M3 at Micheldever Station, filling up halfway back to London.
That was a super fun day, save for the keys to my bike locks falling out of my pocket somewhere in Somerset to be lost forever. And I had to buy a new lock for my top box as you cannot cut spare Givi keys, and I did not want to risk gong out with my only copy.
Mind, that best recent reading in Suffolk was when avoiding some dirty gravel, I caught a less obvious pile of gravel, fell over, and bent the handlebars.
So I think the lesson I have learned is the better the mpg the greater the price you have to pay.