The statistics below show speed & accuracy on a range of recent Macs (2010-2012 models) achieved with a brand new voice profile in Dragon Dictate. Even though there is a 3x difference in benchmark scores between the slowest and fastest Mac, the accuracy is nearly identical! The only impact is in the speed of dictation as your Mac tries to keep up with your speech. Compared to a baseline typing speed of 60 wpm - generally considered a competent typing speed - you can immediately get a speed boost of 65% to 100% by using Dragon Dictate on any recent Mac.
Late 2010 MacBook Air (Geekbench: 3,000 and Novabench: 307)
Speed: 100 wpm Accuracy: 91%
Early 2011 MacBook Pro (Geekbench: 10,300 and Novabench: 1,145)
Speed: 124 wpm Accuracy: 92%
Late 2012 27 inch iMac (Geekbench: 9,400 and Novabench: 882)
Speed: 126 wpm Accuracy: 92%
These speed and accuracy figures can be improved significantly by training Dragon Dictate. The above post in an excerpt from the ebook "Dragon Dictate: Fast Track to Prolific Writing on a Mac" published in October 2013.