I am about to winterize my Mercury 4-stroke 90hp engine.

Apart from using a stabilizer, is there anything else I should do to
minimize the effects of long duration storage of my boat? It will be
winterized next week and won't be in the water till next
June-July...This means the gas will be sitting in the tank for some
nine months. Since I don't use the boat enough to completely empty the
large 100 litre tank each year, a bit of that gas is from the previous
year.

I read many posts recommending the use of higher octane gasolines.
Is there any reason why the advantages of higher octane not apply to 4
strokes ?

André