Certainly with 'basic' axial flow engines like the RR Avon it was reckoned the sfc was far better with RPMs in the 90's than the 80's (design factor?). Thus it was sometimes 'procedure' on the BAC Lightning to close down an engine when short of fuel (often
) to push the other engine up into the 90's. I also heard 'a story' that the Nimrod shut down 2 on patrol loiter.