The 2600k might be a new architexture but but with Ivy Bridge it will in my eyes the swandy bridge will be replaced. Plus the options for a sb compared to a x58 board in my eyes the x58 board has more options for sound, network, and thats probably because the x58 has been out longer.
The reason I siad that hexacore is future proof is because in my eyes in the future I see more developers, software, and games going to to more a more multiple core cpus, but dont quote me on that.
Anyways the 990x is a great chip. By raising the bclck you do raise the speed of the system, but then you can fine tune it to the faster ram and make everything run in harmony. So the way I llok at the 990x vs 2600k is that you can get performance out of the 2600k but the 990x you can get performance with the ability of fine tuning the fast ram with raising the speed of the system to get a entirely fast sytem overall if that makes any sense. If I have this wrong please let me know as I am still fairly new to oc'ing but this is the way that I see it in my eyes.
But the bottom line in any chip in the right hands is to see how much performance we can get out of it be it a $300 or a $1,000 cpu. B-)