Holy Cow. That bottle is cask strength! You have been gifted with something special. Be careful as it won't take much to lift the top of your skull. If that were mine, I would pour some neat into a Glencairn Glass, let it breathe for 10 minutes or so, and sip it very leisurely. If you decide to put this in a mixed drink, that's your call but I don't want to hear about it.
The Glencairn Glass is what most enthusiasts and folks in the business use for tasting whiskies. It’s the right dimensions and shape to maximize the nose and taste of the whisky. They are cheap on Amazon for 2 and 4 packs. Be sure to buy unleaded crystal / glass when using for alcohol. Otherwise, trace amounts of lead end up being digested by the drinker.
Decanters for spirits are very different than decanters for wine though, they don't even look the same. I was actually wondering why they were still called "decanters". The couple reviews I saw claiming the glasses were fake were on this listing, one person even had a picture showing that the font for the etching in the bottom was completely different from what the company behind the Glencairn actually uses.
I use glencairn glasses like this: https://www.amazon.com/Glencairn-Crystal-Whiskey-Glass-Set/dp/B00H143UXW
I am thinking maybe that glass is intensifying the smell which normally I enjoy, so maybe I should just drink it out of a rocks glass neat, and won't get the smell as much, does that make sense?
Fun fact (for those in the US and buying on Amazon at least): while buying 2 puts them at ~$7-8 each[1], the sweet spot is usually in 6 or 12 packs at ~$5 each[2].
[1] https://smile.amazon.com/Glencairn-Crystal-Whiskey-Glass-Set/dp/B00H143UXW/ [2] https://smile.amazon.com/Glencairn-Crystal-Whiskey-Glass-Clear/dp/B003VAWA68/
I just got mine from amazon, got the two pack for $18 a few months ago.
OP's glasses are not too bad looking for whiskeys tbh. It will work nicely with a really high proof dram. Why not pick up a set of 2 or 4 glencairn's to go with current glass set as a just in case. You can get similar looking glencairns as well but they cost a lot more. OR not worry about it, i like having different glasses in my collection so maybe this person will too.