It is worth noting that the typical Scotch Whisky drinker in Scotland usually adds plenty of (not too cold) water to their whisky. Usually an ounce of water to an ounce of whisky.
I, however, prefer to go a 3:1 whisky:water ratio. My years of drinking bourbon neat have trained me for this.
Cask strength whiskies are a bit of a trick, though. I think the best way is to experiment for yourself-- everybody's pallets and nasal sensitivity are different, after all.
For cask strength whiskies, I will usually start it neat to get one flavor/fragrance profile, then dilute it to 3:1, then 2:1. I'll usually drink the bulk of it at 2:1.