My '10 XKR will show high 30s mpg if I reset the trip meter while cruising at around 40mph. In real world, daily use though it averages around 16mpg.

 

I used to get 99 mph in my old F150 with a 5.0 Coyote. I reset the indicator while coasting down long hills.

 

In my 2013 XKR vert around the city with intermittent freeway driving I average around 17.5 MPG. Out in the Country at 75 to 80 MPH I average 22-24 MPG
In my XJR 2018 575 around the city with intermittent freeway driving I average around 22.5 MPG. Out in the country at 75-85 MPH I average 25- 27 MPG.

Both cars are SC 5.0L. The XKR has a Mina exhaust back box. The XJR is strictly stock. I find that I tend to drive the XKR harder and the XJR more sedately.