If they are the same shipped with cooler master cases (stacker or elite) they are good at 5V I'm using five of them among my computers both in vertical and horizontal position. One is running in my main PC and I can't hear it over two 8cm Nexus at 5v, but I think this is a particularly good sample.
Just to make things clear my Slipstreams 1200 at 5V are not as quiet as these ones.