My old 4m Searider / Suz 25 (1993 ish vintage 2- stroke) Averaged 0.76L / nautical mile over a season's use. That includes a week of use as a rescue boat where it sat at tickover with lots of stop / start.
The one cruise (Approx 45 nautical miles) I have hard data for gave an average of 0.73L / nautical mile. That was 2 up, and with quite lumpy seas on the way back, so I guess about 1/3 of the trip was done at 3/4 throttle. Rest pretty much flat out as I was trying to keep up with a 50!
Hope that helps.