Generally, too much is easier to deal with than too little. But don't make the mistake of several folks I know and deliberately run too stiff of an arrow. You try to get as close as you can to ideal, and if you have to choose, err on the side of a little too stiff. Adjustable draw weights, different weight heads, and the latitude to cut arrow shafts to length has always given me the ability to tweak the spine to a nearly ideal stiffness.