Unfortunately, this discussion appears to show that too many people who fly public transport aircraft have a poor grasp of safety, performance, economics and common sense. Fact: Modern performance is designed so that there is a margin built into the numbers to ensure the average pilot, in the average aircraft (actually I believe it to be the 1 in 1,000) with half the reported headwind or twice the tailwind etc. But exactly how the numbers are actually generated is not our concern, we just have to make sure we are up to date with version numbers. But whatever numbers are produced, some companies insist on an additional margin. But with or without an additional margin, if your performance calculations show you can depart from runway X with a given set of conditions then you can, legally and more importantly, safely. Furthermore, the real world clearly demonstrates that additional DIY margins add nothing to safety because if they did, they would already have been mandated the manufacturer and/or your regulatory authority. I'll give you that performance computers often come up with interesting numbers but dealing with those is a different subject.
Therefore, your decision on which runway to use must depend on your company policy on derated/flex usage balanced against operational considerations. And achieving that balance is what we are paid for.
While I'm here, this discussion shows an interesting paradox. There appear to be some posters who will only use the long runway, for "safety reasons" and people like me who are more than prepared to use the short runway. So if I flew with one of the former, we could end up arguing over "safety" and actually compromise the real safety of the aircraft due to an argument. It's the same argument as minimum fuel one and I bet the same players are the same!
PM