All depends on a lot of variables. Summer will yeld a larger difference that winter, traffic conditions and driving environments have a major say in the difference --weather also.
In a car as heavy as my TCH (and I suspect in the NAH also) I find that some old hypermiler techiques like P&G are either impossible or are simply not relevant in any realistic driving scenario. That said, there is a significant difference in FE depending on how you define "hypermiling":
1. Do you use target speeds or target FE values (by gauge) when hypermiling? .. and how well do you stick to them?
2. On hills or grades, are you patient enough to accept a loss of speed (UP) or to back down (down) to those target values to mimimize use of the ICE
3. Do you anticipate stops, decelerations, and accelerations to the same extent for both "modes" of driving?
4. Do you route plan to the same extent in both "modes" -- particularly when one route option may have demands for lower efficiency due to higher traffic densities and more stops and starts.
5. Are you willing to accept "social pressures" in traffic when hypermiling? ON a recent trip to the coast, my 58
MPH target speed showed 44-46 MPG on the gauge (proved by fill calculations), but on the Washington highways that got me there, the average speed over short segments was probably well in excess of 70
MPH for some of the cars that passed me and they would probably number in the several hundreds. I did get there 20 minutes behind some of them. That is not always easy to accept in some social situations.
My reward was 45.2 MPG vs a very probable 37 MPG. A savings of slightly over 5 bucks or 1.3 gallons for the 354 mile trip (just over half a tank). Time lost, less than 20 minutes for the day trip of 11.5 hours total or about 6 hours of driving. Worth it? You decide.