I recently purchased a 120x120x35mm fan that spins about 3000 RPMhttp://www.newegg.com/Product/Product.aspx?Item=N82E16835185054
The fan is absolutely amazing for the price. My GPU temps drop nearly 10ºc when the fan is on. The only problem I have with it is the noise. It truly is louder than most home fans lol.
I'm thinking of returning the original fan I purchased and buying a bigger fan with about 1500-2000 RPM. I assume the airflow will be very similar considering the blades are nearly 80MM larger.
I was thinking of grabbing one of these http://www.newegg.com/Product/Product.aspx?Item=N82E16835146003