You must remember even though sandy bridge as been out a long time.. a 2600k still stands up on its own again most of Intels latest line up.
You got Ivy what was a complete disappointment and horrible for Overclocking and temps. a Good overclock on a 2600k a ivy i7 wont match it even if you was to try and match it overclock.
Then you have Haswell with better cooling but on about 10% improvement. Still not worth the CPU upgrade
Sure things would improve more if I was to change to 2011 but that is a big cash pocket for me willing to go that far.
x99 around the corner also, if the prices are right will be a great time to upgrade.