Problem with Speedfan is that they don't actually tell with 100% accuracy which fan you are slowing down unless you got a see-through window/case or you've marked which fans you are slowing down, because if you just start randomly slowing fans down, chances are you might slow down a graphics card fan and then you forget you've turned it down and you start playing a game or something - then you won't be too happy anymore. So watch out for stupid stuff like that.