The new Scythe Slipstream fans definitally run cooler than the older ones I had in my case (Uhh, can't remember the modelname, they were the original ones with Sony bearings). They dropped my CPU temp about 7 degrees (very obvious drop from 59F load to 51 +- 1). I replaced all 3 of my fans (in, out, cpu cooler).
Edit: and definitally less loud