I'm not sure if I'm following, but it sort of falls into the same hat. If we keep it strictly to the dogmatic type then you're not going to see much difference in average intellect between the type who adheres to the Bible and who adheres to the Communist Manifesto (for example) as unwavering truths.
To me, it's not a matter of what you believe in but why. Anyone who can back up his beliefs and opinions based in critical reading of these texts is always going to be smarter than someone who can't. I don't think it matters one bit whether it's a belief in a deity like God or a personality like Stalin. Both can be religions but neither is always a religion. Likewise, one is theistic while the other is not. How smart their followers are doesn't really factor into it because it's so dependent on their level of skepticism towards these 'truths'.
On a personal note, I can say that there are more than enough Christians in my social circles but I don't know a single one that believes in dogmatic crap like the Ark or a young Earth or homosexuality being a sin or any of that nonsense. And two of them even happen to be ordained priests with Master's degrees in theology. All of these fall into the religious camp but it certainly doesn't prevent them from being critical and intelligent people.