The Versa owners manual recommends "regular" or 87 Octane fuel for the V'sthe only reason I suggest that you try the next grade up...'Mid' or 89 Octane, is that the Nissan Dealership is using the mid grade for mpg tests and is also using the same brand and the same pump every time, to try and take some variables out of the equation.
Run out the fuel you have in the tank now, and then get a fill-up with the mid-grade (89 octane) at a gas station that you can use all the time. Preferably a Chevron (IMHO)
This is not Gospel...it's just an experiment. Remember when you stopped filling, and then do the same routine next time...i.e. stop filling at one click- off, or 2 click-offs it's up to you...just establish the same refill routine, or your MPG calculations are meaningless.
Also, don't try to do an MPG check after only 100 miles or so...run the tank down to at least half. My Versa will throw huge MPG's on a light top- up for some strange reason, but when the tank gets down well off the 1/2 full mark, then you have somthing to go on.
On your upcoming long highway trip, take note of the wind speed and direction...a good tail wind will make my V' seem like it's making gas...but a strong gusty head wind will make the gas gauge drop like a rock.
In either case MPG windy readings are pretty much useless for comparison.
Solid information on the "Break-In" period is equally confusing, everybody has an opinion, but no consensus, conflicting advice, Old Wives Tales and Dealership Misinformation.
There is a website, hosted by a very sincere and knowledgable mechanic, that claims break-in periods are a MYTH! He says engines experience run- in at the factory, plus micro polishing techniques mean that the motor is probably set in after the first few test drives...not long extended periods.
http://www.mototuneusa.com/break_in_secrets.htm
My 2 cents worth is this..on the first oil change I installed a magnetic oil drain plug. When I took it out on the next change it looked like a big fur ball.
On the next change, it was covered with more debris, but a lots less, then on the next 2 changes it came out with just a grey smudge on the magnet.
This indicates to me that indeed the engine was making lots of cuttings during the first 3 to 5 thousand miles...now it has tapered off to just a very fine powder-like material that actually disappears when it's touched.