Hi Terry
looking at them figures i think you should be hoping to run at about 4000 to 4200 for optimum fuel economy just ease back a bit it will only take 2 mins more to reach your mark :thumbs:
as for the oil usage i used about 350 litres of fuel at weymouth and used about 2.5 litres of oil but on your figures it looks like your engine is running at about a 30:1 ratio but they also say about them been set up for running in at about 30:1 so maybe it needs altering
as has been mentioned before about the Etecs they use nothing in two stroke oil but that engine of yours seems to be using a little too much
I would chat to a mariner dealer and find out what it should run at and then if it is way too hi then take it back to where you got it from second oppinions sometimes are whats needed
Ther is some stuff on here about opti's but the Yanks seem to only claim a max of 50 to 60:1 ratio
http://www.thehulltruth.com/boating-forum/165877-optimax-engines-optimax-oil.html
also look on here there are some details of OPTI's doing 100:1 ratios
http://www.wmi.org/bassfish/bassboard/boats_motors/message.html?message_id=223370
Have you thought of buying in bulk the guys below will do a good deal
ETEC (little oil)