Having drunk single malt whisky, and it's the only spirit I drink, for about
30 years, I have come to appreciate the beauty of cask strength whiskies. (I do have Japanese, Irish and Welsh single malt in the house, but never sampled the New Zealand yet.)
My personal preference is always to serve at room temperature, never with ice. I always pour neat enjoy a couple of small sips, then add a few drops of highland spring water, to bring down towards normal strength, and give a whole new whisky to taste.
I normally drink standard tap water, but my whisky I treat reverentially. As I pay on average about GBP 45 a bottle, it's too valuable to treat in a cavalier fashion. That's not to say that there are not plenty of good 40% ABV bottles around. I always have a few in the house for the less discerning palate.
Unfortunately since I gravitated towards cask strength, and also retired I can now no longer afford to keep a bottle of each distillery in the house. So eventually I will be forced to stock only my favourite 20 or so.
Roger