Stick with your stock fans, I think the only difference is the blade colors and frame design. As for the cougars, as much as I like lighting, the cougars have less than half the SP of the Corsair Fans.
Update: Corsair's page says that the H100i fans have a static pressure of 4 mm/H2O, and their SP120 run at 3.1mm/H20. Stick with the stock fans, those are really really good.