My aluminum 37 ft. Roamer (37-2509) uses lots of fuel. From memory, this is my best recollection:
6 knots 3 nm per gallon
22 knots 1 nm per gallon
30 knots 0.8 nm per gallon.
I might be a little off on these numbers, but this is my recollection, as calculated on the Garmin GPS connected to fuel flow sensors. I've heard other people say that these boats burn 30 gallons per hour. This seems to be true, at a nice cruise speed (22 - 25 knots).
My boat is configured with twin 454 crusaders, 22 x 25 props, and 2.57:1 reduction gears. I typically run the boat with less than 50% of full fuel capacity in the tanks, and only enough water for flushing and other needs.
I don't (yet!) have trim tabs, and I expect this will add a bit more range per gallon.
Given all this, I'd say that you can be certain that your roamer fuel consumption will be "every drop you put in her."