3770k about $290 - Selling your 2600k. 2600k used about 1/2 of what you paid for it = about 150 for new 3770k.
I'm quessing you did check if your MB will take SB CPU, I have the Z68 and Asrock just came out with a Bios update that "says" adds IB support.
If The 3770k is not on support list, then a NEW MB is also required.
OCing your 2600K depends on your MB - Does it Support OCing.
If it does, then a mild OC is normally as simple as loading the MB utility that will auto OC the CPU. MB utility is NOT as good as manually doing it as they tend to be a little aggresive on Vcore Voltage.
Normaly a mild OC will NOT decrease the ife span below it's useful life expectance.
My 2500K went to 4.8, but backed off to 4.2 using the Asrock Utlity then I simply went in to bios and lowered the Vcore manually.
AS to getting the 3770k when you have a perfectly good 2600K is NOT worth it. As others pointed out the performance gain is <10% and that is for the CPU, system performance is lower and it takes about 15% gain to even notice the performance increase.