The best I've ever gotten was 28.5 hwy, all stock '09 with 87 octane and a/c turned off. I generally avg 20 city/ and 24-26 hwy depending on what MPH I set the cruise at.
That's measuring mpg the old fashioned way too, I don't trust the electronic gadgets to be very accurate for mpg, they usually just "infer" the amount of gas consumed by interpreting data from the engine. Sometimes they're pretty close but other times they can be off 3 or 4 mpg.
I knew there wasn't great difference in mpg between the 4.6 and 4.0. My choice of a V6 car was due to purchase price not MPG, but with as much as the price of gas went up since I bought the car I've been salivating over the new 3.7, 100 more hp AND better mpg, what a deal!