“Sweet Spot” in RPM for 2017 Sprinter 314CDI 906 OM651 ?

[Wildcamper]

Hello
What is the sweet spot in RPM for a Sprinter with OM651 engine?
In terms of best fuel consumption and mechanical sympathy
I prefer to travel at 60 mph on motorways, it seems counter intuitive but is it possible to achieve better mileage to drop down to 5th gear to boost the RPM higher to about 2000 RPM?

 

[ajlsl600]

My 0m651 sweet spot is 75 mph 2000 rpm 36/37 mpg
Andv65 mph about 1800rpm and 39 mpg in ml250 bluetec.

 

[Wildcamper]

Thankyou ajlsl600
Apologies for late response
I kept forgetting to note the RPM that my van seems happy at
1750 RPM equates to 60MPH and records a better average fuel consumption than at 2000 RPM
And I can travel at my comfortable speed, after years of towing a caravan I find 60MPH relaxing and economical