At your electric cost, don't even bother looking at the S7. It is very marginal on IF it is profitable right now at that electric cost, and WILL be unprofitable long before it can repay it's purchase cost.

 S9 is profitable, even at that electric rate - but it's VERY iffy if you'll make back the purchace price on one at THAT high of electric cost.

 You might be better off looking into the A4 Terminator, as Litecoin pricing has been a lot more stable and profitable consistantly than Bitcoin has been the last year and change and even the introduction of the A4 shouldn't drive Litecoin difficulty up a ton in a hurry.