Personally i took the shroud off and mounted the 120mm fan provided with the Heatsink directly to the fins.
I got this idea the other night, but im not really sure how well it would work.
I want to test out mounting an Aluminum 120mm fan to the Rosewill Z3, considering the fact that Aluminum conducts heat better than Plastic

Im just curious to see the results. However, im quite sure that there will only be a 1 or 2 degree drop in temps..
I guess the question is, when is surface area to much??
Honestly i want to mount 2 120mm Aluminum fans both blowing to an exhaust fan, I'll test this out when i get my Antec 900.