MPG has more to do with commute length and terrain than anything. For example, if I were to live two miles away at the bottom of the hill I'm on instead of the top, I've calculated I'd achieve 5-6 MPG more every single tank. The difference would be more extreme if I made only short trips. Next after commute length would be driving style. Changes like tire pressure are further down in terms of significance.

I found going from 30psi to 44psi (max 51) nets me a few extra MPGs, better road feel, in exchange a bit more noise and bumpiness. I'd reccomend just nudging up the pressure until you reach the highest point where you're comfortable with the ride/noise level, and sticking with that. I've gotten quite used to 44. When the dealer reduced the pressure after getting a software update, I noticed that the car decelerated far slower when cosating, forcing me to stay on the gas more in lots of situations. I also prefer the handling with a bit more PSI.

I've tried pressure at 51, and driving obsesively to maximize MPG at one point but got tired of it. Now I drive efficiently but not obsessively, and cut back presesure to 44psi. I achieve about 4-5mpg less, but enjoy my driving a lot more.

 

right now, 39 PSI all around, which is the highest i've gone so far, probably go up a little more...

 

I decided that mpg was important but "ride" was too so opted for 38 psi.
At my automotive store I found a dial type pressure gauge which came with valve caps which showed green if the pressure was above 35 -38 psi and showed red if the pressure dropped below 35 psi. At a glance you can check that all the tires are in the right pressure range. The valve caps are very small and have a clear plexi tip which shows green if the pressure up and red if it is below 35, The store also sells the gauge in two other pressure ranges, both lower. On the box it said that the 35 - 38 range set was for minivans.

I also bought a small compressor with a storage tank so that there would be no problem in checking and filling the tires of our vehicles.

 

I do a Stock pressure of 32 PSI and get 55.7 mpg on my 38 mile commute to work. I'll test bumping it up a little bit this spring but i think people always want to feel like there doing something extra to feel better about their results ... i think the manufacturers numbers are best.