My JD 240 with 14HP kawasaki is about 1 gal per hour. It takes me about 2hrs or a little better to mow, and I can mow twice and it's all I can do to squeeze a 5 gal can it.
My bota 3400 is about 1gal per hr as well.
Dads 61" ZTR with 23 HP kaw is somewhere between 1.5-2gal per hour. But considering it mows 2x-3x as fast as my 240, he is actually using less fuel per acre.
Another note, the 8n we have only consumes about 1 gallon per hour as well. I think that was a big selling point for them as well, being able to pull a 1bottom A WOT one gallon per hour. It also has the sherman tranny so it will do about 25MPH. Given that driving on the road isn't as much load as pulling a 1 bottom, that is somewhere north of 25MPG on 60 year old technology. And considering it uses about half the fuel as some of these small mowers with little briggs motors, and it is way more tractor, are we going the wrong way with technology???