I don't feel that any additional distance is really necessary to say with some confidence that, for example, 2015/6 is probably not the equal of 1966/7 when it

I don't feel that any additional distance is really necessary to say with some confidence that, for example, 2015/6 is probably not the equal of 1966/7 when it comes to pop music in at least the English-speaking world; and I wasn't born by 1967. I can't think of any years in my youth to compare to 1966/7 either, for all that I too admire and fondly remember Nirvana.