Mark Liberman assesses the candidates by speaking speed.

Overall, the Republican candidates are about 4% faster on average; but an unpaired t-test on the candidates' rates suggests that this difference is not statistically significant. It's perhaps worth noting, though, that stereotypes are not in general confirmed: John Edwards, despite his southern drawl, is around the 75% percentile of this bunch. Hillary Clinton, who as a woman should by stereotype be a faster talker than her male competitors, is below the median in this sample.