Not to be, "unhelpful" but it really, honestly truly depends on the person. Can't really say that all Atheists are mid class, and all Christians are higher or lower. In history, we usually notice that those who are of less income, usually cling to their faith (which isn't always Christian, there are other religions besides that one), because they feel in need of help and they have no where else to turn. However that's not always true, because the same situation could make someone hate the idea of any god, or just not acknowledge it. It really depends on the person, time, place, environment, etc.