As an atheist, I never gauged somebody's intelligence based on their religious beliefs, and I do understand that a religious scientist can make amazing progress for humanity. The thing is, most of these scientists tend to be very moderate, and even though their very life work might reveal things that contradict religious scripture, they still hold onto those beliefs. I will say that fundamentalism (focusing more on the Abrahamic religions) probably isn't compatible with science, because if you take most religious scripture at face value, it simply doesn't mix well with how the universe actually works.