Depends...do you feel lucky punk? Well do,ya?
Am I wiling to go into a strip that has available the same amount of runway that I require? I doubt it, unless it was an emergency. I like somewhat of a fudge factor, maybe 20-30 % added to the required length. If it is the difference between actually getting a client into his destination, I will consider the alternatives in the area, and if the terrain allows an approach to land on the numbers, but I don't look at less than 15%.
This would obviously be Adapted for the prevailing conditions. If its rainy and wet, I like to look at the factored numbers as a sensible guide to what is expected. I just feel that I don't want to have to answer questions like : why did you slide off the end of a wet runway that was shorter than your factored wet distance required - even on a 91 mission, I think you will have some 'splainin to do.