[RedDevil]

I'm happy with 45 PSI on my narrow winter tires and found the car handles better on it than with lower pressure. The wider summer tires lost a bit of their rolling quality onder 45 PSI so I may run them slightly lower, but we'll see. The make and quality of the tire is an important factor too; on all my previous cars and bikes FE (and grip, ride quality & tire longevity) went up by changing the OEM tires for top spec.

Although I'm ready to take your word that you can accelerate faster at 45 PSI than at 55 PSI, I wonder what could cause that (other than tire circumference and tire skidding?).
Btw. I think that measuring acceleration is not a very precise way of measuring the effect of tire pressure on FE.
The factor that contributes most to FE while dependant on tire pressure is rolling resistance. The best way to measure that is by coasting down at a set point and speed and measuring the remaining speed at a fixed point further down the road.
Do that repeatedly on the same day with different tire pressure, or do it daily on your commute and build up a big sample to get your data from.
If you can do this at reduced speed then the differing air resistance due to changing weather is less of a factor.

I found getting reliable test data is very hard. I tried to test the effect of lower grill blocking and WAI, but the data is all over the place and it is hard to make a point from them. Do one test and it fits what you want to believe. Do more tests to quantify the gain, and suddenly the opposite happens...
The only strong conclusion from all my testing was that side wind is worse on FE than wind straight ahead. I wasn't looking for that but it kinda forced itself in. From aside.