As a matter of professional respect for fellow computer engineers, I can't buy an ES chip and wouldn't recommend buying one either.
As said before, this could be a huge risk. It might be a good enough chip or it might be one of the first 980x's and have tons of flaws. The only way to tell is to ask Intel and I can tell you they are not going to tell you and will request their chip back (no compensation).
ES Chips are for testing both internally and externally. Usually these chips get onto the market when external testers don't return their chips and then sell them (which is why I have a stance against buying and recommending them - outside of the risk). That essentially makes them stolen goods.
If you are someone who doesn't care (I can't blame you entirely) and is willing to risk the chance the chip is basically junk (if you run heavily threaded applications, having a 980x would be a great idea), then you should infer the obvious.
I personally don't think it's a good idea because chips like this can come seriously under-clocked and next to impossible to get up-to the clock speeds that make a 980x really worth it.