I'd go for the 2600k. Or 2500k even unless you expect to run a lot of transcoding and rendering or other heavy thread optimized software.
It's just hard to beat the value in SB i think, seeing how easy they oc and the temperatures are so easy to keep under control.
IB will work just as well though heat will be the limiting factor making both options about the same in net performance.
I'm assuming you will oc as you mentioned K model.
OC or not, they are good value and great performance
Asus(Z68 and up) or Asrock (if you go with Z77) mobo to go with it. Though personally i'd go with Asus, their lineup from lowend to highend have pretty much the same UEFI features for oc and stability, the ability to offset overclock is great too. It's also very fast and responsive and logical layout not too different from the old bios we are so used to. So it's really just a matter of what features you require on the mobo.