Atheism does nothing for your intelligence, your ability to reason, or any other mental faculties.
Atheists and theists occupy all points of the IQ range.

Many intellectualls throughout history and modern times were religious, or at the least, theistic. For example:

In addition to high-IQ intellectuals, there are many scientists, living or dead, who are religious or at least believers in God's existence. Some of these scientists are responsible for significant modern achievements and breakthroughs:

Religious scientists are more numerous than militant atheists are willing to admit. The British organization Christians in Science has over 650 members. Even more telling, a recent survey found two-thirds of American scientists in research universities to be theistic or religious. This study did not examine individual religions or the scope of which the scientists were theist, but merely their belief as to whether there is indeed a divinity.

LiveScience Article
Washington Times Article

"My view of things is that evolution is too elegant for God not to use. A lot of people I know were surprised to discover that in addition to having a degree in molecular biology—and working on another in physics—I am very religious. They have problems squaring that circle. How can you be a scientist and believe in God? is the question. Very easily, from my point of view. I see the Universe as being like a house. Science can tell us what the house is made of, it can tell us how the house was built, but it cannot tell us why the house was built, or who built it. Only religion—or in the broader sense, metaphysics—can do that."
- Joseph White, websnark.com