The fan I'm using circulates the air just enough to keep the temperature even throughout the smoker. I put a fan speed control switch on it but really didn't need it. I'm not sure what the RPM is of the fan but I could try and find it out for you. I bought a fan with a shaft long enough to go through the wall of the smoker. My wall is insulated and is 1" thick.
Let me know if you need anything else. I've been using the smoker steady since I've built it and made just a few mods to it. It works great.