Exactly. Chances are, there is a good reason as to why it's only an Engineering Sample instead of a retail chip. Seeing as to how these were made before the retail chips were actually introduced, I'd steer clear of them in fear of something similar to the pentium bug that happened a long way back. On the other hand, you may get a working 980x, but from what I've heard and seen, getting an ES is like buying a triple core CPU and hoping to unlock your fourth core - it may be possible, but don't get your hopes up.
Just my $0.02.
Think of it as a beta version of a CPU chip. It's a pre-production, limited quantity sample distributed for inhouse testing and hardware and software development.
Yeah exactly. My friend got an engineering sample on ebay a few months back. It came stock 2.0GHz, I believe, and he upped the multiplier to 25 to make it 3.33GHz. I tried to push it a bit further but Prime95 complained and I didn't have time to do anything like voltage changing or trying lower frequencies (just tried to go straight to 4GHz).
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.