I believe the reason it says "None" for effect, when typically an item with no effect just doesn't say anything, is because through a quest in the Plane of Air (Sky, whatever) the Silvery Girdle gets "upgraded" to the Girdle of Faith, which is basically the same belt, but with either a 36 or 41% haste (don't remember which). The two other items needed for the quest are noted in a post below. This belt is not to be confused with the other dropped haste belt in Plane of Air, which only has 16% haste.
Note that this is the common drop needed for the Paladin haste belt from PoA. You turn in the silvery girdle along with a diaphanous globe and an ivory sky diamond to get it.