The fact that you are asking if "overclocking is worth it" probably answers your question.
Whether or not you OC is probably dependant upon what workload you undertake, how much you like tinkering, and if you are working under some very tight time constraints - the latter is more applicable to content creation and media applications.
Personally, from the price difference of the two models, I would go with the 2600K. Pricing difference is minimal, and resale -if you plan to upgrade in the future- will be higher. So even if you do not plan on overclocking, the 2600K makes a degree of economic sense.
For most users I would think that Sandy Bridge's turbo option (think of it as automatic overclocking) will suffice. If, however, you want a little free performance- virtually every 2600K will attain a higher 24/7 frequency for little or no extra power draw/heat output- or you want to explore the CPUs performance parameters then
light or moderate overclocking will cause no harm so long as you observe some basic procedure. Even motherboard based overclocking ( hardware and/or software) will offer a substantial performance boost (application dependant) with stability and a minimum of user input.
An overview of what Sandy Bridge overlocking can achieve >>
here<< and >>
here<<
Be aware that overclocking the CPU impacts the RAM (memory) speed as the two are linked via memory dividers ( CPU: RAM ratio's). For overclocking purposes -even the one-click (software) or one-button (hardware) variety- you would need to have DDR3-1600 modules at the least (with DDR3-1866 for high overclocks which I would not recommend if using the boxed Intel cooler).
If it sounds as though I'm fence-sitting, that's because I am. I have overclocked virtually every component I've ever owned that was capable of being overclocked...but then, I
really like exploring the capabilities of a system I put together - both from a performance aspect, and judging long term stability.
I presently run two systems, an older Core 2 Quad and a X58 based system. The former runs at either a stock (undervolted) or with a mild overclock (25%) using only stock voltage. The X58 runs at either stock* (again, undervolted), mild OC¹, medium OC² or heavy OC³. Virtually every motherboard these days allows for multiple BIOS/UEFI profiles to be saved as used as appropriate- so you can run the profile that best fits the application(s) you plan on using. Using these different profiles over the same applications then gives you an accurate "hands on" guide to any worthwhile gains you may experience- as opposed to online reviews which may use benchmarks (especially synthetic test suites) which may be of only academic interest.
* Stock for average mixed workload- browsing, email, media viewing
¹ Mild OC - Benchmarking for scaling performance in new applications or major revisions to current applications
² and ³ Med./Heavy OC for intensive applications ( media encoding, achiving (compression), gaming etc.)