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OP last ages, the tread itself wear a little quicker but after that, it'll last for quite a while.
Mine's about 4,300km and only the very middle is smooth.
Don't forget @skinny probably got the most out of them at 8,000km and counting.
Unfortunately they're no longer making them and getting replaced by the new Vittoria Corsa that also come in 28mm and apparently got an "amazing" puncture resisting ablitiy.
What's the tyre of choice for British winter riding (alternative to OP as they are great but probably wear a tiny bit too quick) in 28c?