Paul,
I've always used the ECO mode so I don't know what the difference would be.

My normal driving is heavily slanted towards highway use.
It's 18 miles to work and 15 are on the tollway. In 70F weather if I'm not running the A/C or the heater I can easily get 40+ mpg on this trip.
I get the best highway mileage at 55 mph. One time when I filled up and drove 63 miles on the highway my tank average was 47.7 mpg.

30-35 mph is also another good mileage speed. Once the engine is warmed up you can drive a couple of miles in EV mode at 30-35 before the engine starts to recharge the battery. I use moderate acceleration to get up to speed, take my foot off the accelerator to kick it in to EV mode and lightly touch the accelerator to use the battery to maintain my speed.

Short trips are horrible. One week where all I did was drive to and from the train station 2 miles away my trip display never even hit the 25 mpg mark. Also, just going from stop light to stop light without some distance between them to get into EV mode will hurt.

I have the Bridgestone tires and have them at 35 PSI.

That's what I can tell you but in summary, longer trips at constant speeds (cruise control works fine) will help your mileage.