my next boat will have a 4 stroke, will go mercury, price for PM on a 4 stroke is about the same as the oil you will use in an opti, and the new 4 stroke only weigh about 25lbs heavier than the 2 stroke opti and mercury makes their own now with good results.
Brent at performance will tell you to go with the (company made oil) they know what is needed he also says most two strokes don't get cold enough here in AZ to thicken up the oil where it will not pull the oil up for use