On the topic of magnums..
Speaking with a friend who works as a vit he reckons that magnums are more bad than good - for pretty much the reason you've alluded to above. Because they are large they are mishandled in transport, and people treat them as a curiosity and display them rather than cellaring them properly the way they might treat a standard bottle (his favourite being people who put them on shelves behind bars where sunlight falls on them, standing upright so the cork dries out, or better again, on top of fridges)
No doubt you'll then choose to open it for a special occasion, which will make the disappointment all the more memorable for you and your friends, forever tarnishing your opinion of the product.
But.. people keep asking for them, and you cannot ignore their demands indefinitely.
Ahhem, back to the question..
it ages.. up to 10 years I've read favourable comments, there'd be better people in the forums to ask than me - the longest a chimay blue has lasted around me is about an hour.
