How to record a slide presentation efficiently with video/audio
Using one of these solutions will be more efficient. That's what you've asked for. It saves you time, because there's no more need to manually sync the presentation and the voiceover. 

Free Solution


Keynote can record a running presentation with the mic-audio. 
QuickTime X has also a screenrecord-feature incl. audio.


Low Cost Solution


Specialized screenrecording software like ScreenFlow, Camtasia, Screenflick, Screenium, etc. 


Pro Solution


Capture hardware like Ninja Atomos, HyperDeck Shuttle, Intensity Pro, Aja IO, etc., can record directly with ProRes-codec.


A professional solution with capture hardware can record directly in Final Cut Pro X (and other NLE) native codecs/formats like ProRes422. This saves a lot of time and discspace. The picture and the audio will be always in sync, and in addition you'll get a recording with smtpe-conform timecode. – There are even more advantages, but they will be more important if you record live presentations.