Dragon NaturallySpeaking is the quickest way to get single speaker audio transcribed into a document. The software is really quite amazing and it recognition characteristics are phenomenal. However, some things outside Dragon NaturallySpeaking can slow it slightly, especially on older lower spec PCs.
Here is a tip for you, if you are finding that your dictation using Dragon NaturallySpeaking is lagging slightly when you dictate into Microsoft Word this is generally caused by the overhead of Word trying to spell and/or grammar check your dictation as it is written. If you have a well trained NaturallySpeaking profile you might want to try dictating straight into Notepad or even Wordpad, you will find that NaturallySpeaking dumps out your text alot quicker and smoother allowing you to talk even faster.
Once you have verbosed yourself into Notepad simply copy and paste into Word and let it do its thing with the spell and/or grammar check.