We'll never truly know, but perhaps the best accomplishment of the Vulcan (and its contemporaries) is the fact that we're still here today and its presence and abilities helped keep the Cold War from turning very hot.
Had things turned out badly I have no doubt it could have stuck a severe blow to the Soviet Union; but then we probably wouldn't be around having this discussion.
I am sure our Royal Navy and their submariners might disagree with that observation and was the Cold War a case of boys with toys all trying to out bluff each other?
How big a contribution would we have made to any nuclear holocaust as my thoughts are that it would have been very little to none as we would have been playing catch the missile within minutes of the kick-off?