This week's book giveaway is in the Mac OS forum. We're giving away four copies of a choice of "Take Control of Upgrading to Yosemite" or "Take Control of Automating Your Mac" and have Joe Kissell on-line! See this thread for details.
The amont of overhead in performing a simple if operaton is completely neglible. You should concentrate on structuring your application in a logical, easy-to-understand manner rather than worrying about performance and overhead. Then, if, and only if, a performance problem can be concretely identified, you can deal with it in a meaningful manner.