I don't believe it makes a difference. The wine I had in the bottle the longest used 10 yo corks -- I had a 1,000 count bag and it took many years to use up the bag, given the wine I made at that time. Yes, the cork was 20 years old by the time I opened the last bottle. They were plain-jane 1.5" #9 corks.
Currently I'm using Nomacorc Select 900's, which is what the unlabeled ones are. The vendor says they're good for 5 years. My guess is they're good for at least 7 years, as the vendor will undersell to avoid liability issues, and I've seen LHBS advertise they're good for 10 years. I'm not honestly expecting to have much -- if any -- of a batch at the 7 year point, so I don't worry about it.
I've noticed a LOT of the French wines I'm drinking are using composite corks. Some have a solid disk on both ends, others are completely composite.
Folks spend a lot of money on premium corks -- I question the true value. OTOH, it's not my money, so I'm not complaining.
