I agree, you should go with the heavier spined shafts. I've always found that I got better arrow flight by overspining a little, even with cut proud of center ASLs. Too, unless you've put those shafts on a spine tester, you don't know exactly what spine they are. If you got mostly high end of one group and low end of the other group, they would be almost identical. Regardless, a few arrows from each group are likely with a pound or two spine of the other, not enough to matter. Tatg's why they fly similarly.
The heavier spined arrows are also likely to be a little heavier physically. And, a physically heavier arrow (because it takes a bit more force to get it moving, which flexes the shaft) takes a bit more spine than a lighter physical weight shaft.