Mate they are a great Motor On the offshore trips I do out to the cape I use between 69-80ltrs of fuel for the day being a 2 stroke you do get a bit of noise but it is bearable and they are very reasonable to service and reliable I have never had a drama with mine.
Here are some vids I have got over time to give you an idea and performance.
Hope this gives you an idea I get about 28-33lph at 4000 rpm but this will depend on the weight of your boat and how loaded up with gear you are to. I am running a 18p enercia prop on mine to which has improved the fuel economy to. Check out the 150hp four stroke to they are very well priced compared to the opti's to. My boat is Whittley 2100 Walk around (6.4mtrs)