Bottom line the newer Sandy Bridge architecture is better. The 2600K and it's platform even uses ram in dual channel with more efficiency than the 980x/990x and it's platform can do with triple channel.
Core for core the 2600k is just slightly less than 10% faster per core and the cost/performance ratio of the 2600k is nothing less than astounding when compared to the 980x/990x although in all fairness that can pretty much be said about any Intel CPU with an X at the end.
Benchmarks are often skewed. Not only are they dependent on the number of threads utilized, they can also be skewed by the test set up. From what I've seen, the test set ups are never equal largely due to the ram. Either the ram amount is the same and one system isn't running in it's best configuration (Dual or Triple channel) or the amounts are uneven and that's just one example. Then there's the sub-conscious (or conscious) desire of the author(s) for a particular outcome.
I have heard that the 980x/990x performance can be improved in some applications by disabling "Intel HT Technology" in bios. That seems like to much trouble to me, I'd rather just give the multiplier a bump without going into bios.
So with money as no object is the 2600K/platform a better choice than a 980X/platform? For me absolutely not. I use some applications for income that can utilize all 6 cores and the 2600k just can't compete and more applications are being written to take better advantage of 6 physical cores all the time. As time goes on and more CPU's have 6, 8 and even more cores this will only become more true.
If I were to build a new system today I definitely would not use the 980X/platform. I would go with a 6 core/2011. The 2600k never was and never would be a consideration although I can certainly see where it could be for a large segment of PC users for a lot of very good reasons.
Since you can get a 980x for only $280 more, you run programs optimized for 6 cores and you already have a complete LGA 1366 platform IMHO I think it's a no brainer. Get the 980X! you'll love it! If you also earn income from programs optimized for 6 cores you shouldn't even need to consider it (any more)!
By the same token if all you did was ck your mail, surf the web and play games even a 2600K would be overkill. As far as the Sata III goes, it's not all it's cracked up to be. I have it and I don't use it because it's to flaky. A regular hard drive can't even saturate Sata II. No (spinning) hard drive can spin fast enough to saturate a SATA II port. I raided 2 Sata II SSD's on my Sata II ports instead of getting a Sata III SSD because it's so flaky. It's flaky on 1366, it's flaky on 1155 and somewhat less flaky on 2011 but, it's still somewhat flaky. Maybe the next generation will be better, it's still fairly new.