I used to use this cooler, fantastic cooling. Because of the RAM being blocked I used just one fan and it was fine. The heatsink itself is so awesome you can just use the one fan and for me at least I didn't notice a change in temps. I think running it passive would be fine provided you got decent case fans.
Only reason I don't use it now is because I switched to water. Now it's just lying around at home...bit of a shame, might sell mine on mm :/