Originally Posted by juicemouse
Are you saying a larger contact patch up front won't improve cornering grip on the road?
And if a narrower tire does not have a (small) aerodynamic benefit, why do the pro's usually resort to 23mm widths? It has been demonstrated that wider tires can have both more grip and less rolling resistance.
Larger contact patch is only a function of pressure, not tyre size. You do get better grip with larger tyres because you can run them at lower-pressures. Tyre size and pressure are independent factors. Although the rounder shape of the wider contact patch does provide slightly more grip than the long narrow shape of a small tyre at the same pressure and contact-patch size. But that's not as great as the difference of a larger contact patch from less pressure.
In the context of the OP's question on rolling-resistance, while splitting hairs is fun, you might as well do it the best you can. In which case, you want to minimize tire-compression. That means you should customize the size for the load its carrying. The larger tyre in the rear will sink and compress less compared to the narrower one when the rider hops on, leading to less rolling-resistance. Of the two possible configurations, bigger in back/smaller in front will be faster (and longer lasting).