I don't use apparel much so not the most knowledgeable person, but I wasn't aware there was more than one piece that offered the same attributes. For example, the SE hat will boost your driver distance and no other piece of apparel does this to the best of my knowledge.
If you're that curious you could always equip one piece of iron distance, go hit 10 shots in practice mode using mulligans, record distances, and then average them. Then equip second piece of iron distance apparel (if there is one) and go through same process. Your answer should become pretty self evident.