The size of the two tanks wouldn't matter if run in series.
The elements are the same wattage. The electrical panel won't know the difference.
Having two tanks means you have twice the recovery. A single 80 gallon has one element working at a time.
With two tanks, you can double that.
Of course, you also have more exterior space with two tanks that need insulating. Most of the time we would just install a single eighty.
Twenty years from a water heater? That's pretty darn good.