I have an magazine(unfortunately in Finnish) with an overview of most common 2 strokes (over here) with some test figures. Tohatsu 120 hp consumption figures:
WOT=52,2 l/h, -500 rpm 42,0 l/h, -1000 rpm 35,2 l/h. Tohatsu was the thirstiest in this test, Yamaha 115 most economical, especially in the -1000 rpm(from WOT), almost 8 litres /h less than the Tohatsu.
Generally speaking, at WOT speed there is not much difference with modern engines and a good 2 stroke(as an example yam 90 AETO compared to modern 90 hp engines). But when You decrease the rpm, difference start to occur.
fun on a boat is inversely proportional to size...sort of anyway