The short answer is Yes.
The long answer involves lots of data and reading.
A study was completed by Tanita (Precision electronic scales) to see if there was a link between proper hydration and performance during Ironman races (and other long events). Over the three years, 4,426 male participants and 1,314 female participants were tested.
By performing a regression analysis, they deduced a relationship between hydration level and finish time - with every 1% increase in hydration, the mean time decreased by .2662 hours (16 minutes) for men and .2036 hours (12 minutes) for women.
For more information (and lots of stats) read the full article here