as I got roughly 1 litre per mile from a 150 Optimax and get the same from my Yam 200 HPDI!! (both fuel injected 2 strokes.) Thats unless I push the loud stick forward at which point my wallet explodes!
On your prop sounds like you might get away with a larger pitch but then again if you load the boat up with fuel, kit and friends then you probably want to stay the same. Might want to switch to a stainless of the same pitch as your ali?
There is a highly scientific method of determining what pitch your prop is. What you do is look at it carefully, muttering knowledgably to yourself and amaze your friends by declaring what pitch it is by reading the number stamped on it somewhere!! I would imagine yours is either a 15 or 17inch if its a three blader.