[aerohead]

I agree that, a BSFC map of your engine is your friend.
* Some BSFC 'islands' can be as 'short' as 300-rpm.
* A delta-300 rpm can alter mpg by 2.85%
* Friction horsepower can increase by 32% within a 300-rpm increase!
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Many decades ago, BMW published the only paper which ever, directly addressed 'transient'-losses associated with acceleration phase resident time.
The paper was entitled something like, 'Good News for Jackrabbit Starts.'
The crux of the matter was that, most fuel is lost during transient engine operation during acceleration up to 'steady-speed' cruising, and that judicious use of the throttle, which gets you 'quickly' up to speed, actually costs you less in the long-run, as you get to the most fuel efficient driving regime the soonest, and for the 'longest'. I think Blacktree and Ecky have spoken to this already.
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* And I believe that, around 80%-load engine operation gets you near max-torque, which also falls at minimum BSFC ( HONDA Motors used this metric for their CIVIC VX reporting ).
* And the 2,500-rpm 'HAS' been reported on with respect to efficiency, as it has to do with the surface-speed of the piston ring/cylinder friction component of the engine's friction-horsepower ( fhp ) losses, which varies as the square of rpm ( why a change of only 300-rpm can increase lower mpg by 2.85% ) [ something not accounted for in the so-called 'throttle stop' engine technique ].