depends. what's your current board, and why the upgrade?
if you already got an OCable board, and have no plans to upgrade the CPU, i see no reason for you to upgrade at all.
if you're seriously upgrading for the sake of USB3.0 or any other ports/features, well if you're unhappy without it and willing to spend, why not?
if you plan to upgrade to an Ivy bridge cpu than yeah, getting a Z77 would be better if you care about RAM speed. most Z68/P67/H67 boards would require you to update the BIOS to use an IB CPU, assuming it's compatible at all.
if you plan to keep the 2600k for a long while, then yes, an old SB chipset is good, better when it is cheaper.