I completely agree with redpoint5 that pushers will never be a solution for the masses, in keeping with the majority of solutions that we promulgate here on EcoModder. My first aircooled VW pusher got a hair over 20 mpg while pushing, and so does my buddy's, right on par with a heavily-laden aircooled VW. A modern ICE drivetrain, esp a diesel should do much better. The equation for lifetime mpg is simple. My pusher usage is under 3% of miles, but let's round up to 5% to maximize the gasoline consumption. My i-MiEV annual miles has hovered at 19k, but I'll round that up too, to 20k to reflect more pushing.
Using the common "Volt driver equation" of gallons burned/miles travelled, if I push for 1000 miles per year, or 5% of 20,000 miles, that would yield 50 gallons over 20,000 miles for
400 mpg.
A road warrior like my RAV4 buddy who lives in a tiny rural town but visits distant places pushes for more like 10,000 of his 20k miles per year, for 500 gallons burned in 20,000 miles, or 40 mpg. That extreme example is past the crossover point for a hybrid or Volt. (Energy-wise, but not based on finances at the time of purchase, and probably not even today if trading the RAV for a Volt.)
Now if we wanna throw electrons into the oily equation, my i-MiEV is rated 112 mpge. Driving 19000 miles at 112 mpge and 1000 miles at 20 mpg yields the equivalent of 219.6 gallons burned in 20k miles, an average of 91 mpg, still waay over a conventional hybrid scenario, and better than most Volts if you peruse
https://www.voltstats.net/. Of course there are Volts with many thousands of miles per tank of gas, but I'll submit that those folks bought some very expensive insurance....
HowEVer, much of this discussion of electric versus gas miles is moot anyway because of the electricity used for gasoline extraction and refining that is rarely included in such discussions. At the Nissan-claimed 8 kWh of electricity consumed per gallon of gasoline produced, an ICE has already consumed 39 miles worth of EV driving power before it EVen starts burning. Any gasoline-fueled vehicle getting less than 39 mpg would be using more electricity than a typical EV! However, opinions are varied as the facts are unavailable on this highly proprietary refinery data that the Federal EIA no longer reports, combined with the facts that even the electricity used in refineries varies according to the cost of grid electricity versus the mix of end-products desired and the current grade of crude oil being input. Here in Washington state, our gasoline is largely refined using electricity produced by hydropower!
Going further, if we consider oil from tar sands, the electric advantages point skyward in a hurry, as the energy required to simply liberate that oil from the ground runs between 20% and 34% of its total energy content...