I would say a lot of it depends on your electricity price.
There is quite a bit of difference on efficiency. What is your electricity price?
Currently around .09c a kwh
I may be moving where it would be .07c a kwh
With current I would say go with the S5. I'm not sure at .07 you might run some math over at bitwisdom, I'm guessing S5 off top of my head but I could be wrong.