I have to disagree that because the Russians drink alcohol would make adoption of Islam ASB. Islam could certainly be flexible enough in its interpretation of alcoholism to appeal to the Rus
From all I know the heaviest drinkers of the Middle Ages were the Mongols.
They even invented the way how to make strong alcohol at home - you take any alcoholic beverage (koumiss for example) in a leather bag and put it out into a winter cold (and we are speaking about Mongolian winter down to -50 degrees Celsius). After some time all water and other substances turn into ice and what is left is pure alcohol/spirit. It was called 'black koumiss' IIRC and was insanely expensive for a poor nomadic tribe.
But after these inventive guys conquered the world many of them could successfully drink themselves to death (alcoholism is the most frequent cause of death of the Genguizzides).
And even these Mongols (to the west from Mongolia proper) adopted Islam as this religion was extremely flexible.
It is a great fun to see how in Hulaguid Il-Khanid Iran the newly converted Mongols celebrated Muslim holidays:
- first three days they prayed and fasted in a proper Muslim way
- after that for three days they drank till they drop in a good old Mongol way.
My point here - even the heaviest drinkers in the world might adopt Islam.
And eventually, sometimes centuries later Islam would/might win against old habit of drinking alcohol.