Oh, yes, most certainly.

Compared to the 1995 8670 Genesis, a 4440 eats more fuel -- about 10% more, by my records.

The machine that really slurps fuel is the 4640, which admittedly is turned up to 180HP, but man oh man, does that 4640 like fuel.

I rather suspect that your assessment is the root of the issue -- the Genesis engine is at 1900+/- RPM for PTO speed, the Deere 40-series is turning at 2200 RPM for PTO speed. Where the Genesis and 4640 are best compared for fuel consumption is when I use the Hesston 1360, 15-foot mower-conditioner. The Genesis can go all day and much of the next on one fill-up, whereas the 4640 needs to be refueled after only about seven hours. By the books, the 4640, before it was turned up, was generating 15+ HP-hr/gal, and the Genesis 18+ HP-hr/gal.

There is no question in my mind that the Deere 40-series machines use more fuel in tillage or PTO work. The reason why I got the two 40-series tractors wasn't fuel efficiency, it was parts availability. When a 40-series machine breaks down, I can get parts from a dozen different sources, none of them Deere dealers.