I don't like the Essence reaver as first item because by the time you finish the item you already are rotating to other lanes for bigger fights (mostly not full teamfights yet but more like 3v3 and so on). Also yo udo more auto attacks there than just throwing out yoru boomerang. I prefer to build Infinity Edge first for this reason. I agree that CD is nice on Sivir though (the 10%).

I'm going to go with the runes and Essence Reaver first just to give it a shot though.