Since TDP is not power consumption, the GTX 1070 will most likely consume less power than your CPU because it has much better power saving features.

Also, since CPU's are idle more of the time than under load the savings by using a newer CPU like Kaby Lake or Ryzen could be interesting. There is also the motherboard. Newer boards consume less power because the chips are on a smaller node.

But I guess the money you saved on buying the CPU will outweigh the electricity costs even in countries where electricity is expensive.