Depends on performance software i guess. The airbus thingy throws out the highest reduction possible, right down to a 1m margin left on the runway. However, it also provides all lower flex temperatures and runway remaining margins for those figures, so take the one with the margin you personally are happy with.
That said, the company wants us to use reduced thrust as much as possible, so if there is no operational downside i would take in that situation the longer runway, reduce thrust a bit and use a larger margin.