I totally agree with you on this. I believe our particular 2.5L SA-G is unfortunately an inferior one from production line, having less stated horse power and hence less fuel efficient. I just hope Mazda can manufacture more engines which consistently meet the specs and discard those which are far off the specs!
With fresh Mazda moly oil and 39 psi on all four tires, I tested out the instant MPGs based on computer readouts during our recent trip to Houston. The computer readout on average MPG is very close to fill-the-tank calculation based on my experience. Here are my data with the best "average" instant MPG I could get on a flat and straight I-45 with steady speed at least for more than 10 seconds:
MPH Instant MPG 55 29.0 60 28.5 65 28.0 70 27.0 75 26.5 80 25.5
Of course these numbers were achieved by manual gas pedal control, cruise control would never get these numbers. And the final average MPG for our 300-mile road trip on I-45 was 26.5.
Really helpful chart and layout. I dig!