I don't know if you need more mana fixing, but Unclaimed Territory can be your Cavern of Souls number five to eight.

I would say Unclaimed Territory would be a fine addition, but with needing swamps for Sedge Sliver and needing green for CoCo, I'm having troubles with what lands to take out. I would say the Gemstone Mines, but again with the green for CoCo, it makes it hard. The only land or lands I can see being replaced are Breeding Pool and Godless Shrine.

Really like the sliver deck and have recently made my own. my Hive Mind deck is super aggressive. I do use a lot of the 1/1 slivers though which I think does offer a certain level of speed I guess. +1 definitely though