I'm no expert on toilets but judging by the sizes of the tanks it's hard to believe there is that much difference in the water used. In any case, you say 1.6 gallons in your text but you use 1.3 gals in your calculations. I just know that I've heard many people complain about how low-flow toilets don't flush as good as the old ones- and having to wait around to flush a second time is certain a imposition regardless of how much water is used.
If you really want to save water consumption you should have all males use urinals rather than toilets for urination as it is very wasteful to use a whole tank of water just to depose of a few ounces of urine. Or alternately- guys could be required to pee into a jug which can be emptied and flushed once a day rather than flushing the toilet every time they go.