Many people do chicken low and slow, just like pork and beef, but it's not really necessary. You're not rendering fat and breaking down connective tissue, which is the forte of slow cooking with tough cuts. Higher heat is therefore perfectly acceptable, and, since poultry is easily over-smoked, a faster cook does not really mean sacrificing smoky flavor. You can leave the water pan dry, and shoot for a cooker temp of 300-350°, monitoring the internal temp of the breast meat. When it reaches 160, the thigh will likely be around 170, at which point you can remove the birds from the cooker, and rest them, tented in foil for 15-20 minutes before carving. During the rest, residual heat will bump the internal to about 165 white/175 dark meat. Cooking white meat to a higher internal risks drying it out, as does cooking too long at a low temp. Brined or enhanced birds will give a margin of error, preserving moistness if the bird cooks to a few degrees higher. Time will depend on the weight of the individual bird. Allow yourself 2 hours cook time for an average size chicken at the higher temp range. Cooking two chickens will not take twice as long, but may extend cooking time over a single bird somewhat due to the time it takes the cooker to rebound to your target cooking temp after adding the meat.
