I just ran a simple regression with Boeing’s latest spec. and the 772LR comes out to be more than 3% more efficient than the ER for a route of 7730nm (772ER max. range). That means that at MTOW and typical conditions, the 772LR will use almost 1400Gal. less than the ER on a 7730nm flight.
Could airlines eventually consider this to be enough to offset the LR higher price compared to the ER?
Of course, we can’t expect Boeing to promote actively the 772LR over the 772ER but that might be another tool for Boeing against their key competitor. The LR version is clearly not going to sell in large quantities for ULH operations but this aircraft could fly «shorter» mission more efficiently than any other plane.