Let me correct you there, (somewhat)..
Ivy Bridge is set to be the final generation of CPUs on the LGA1155 socket, Intel will be moving to the LGA1150 socket early next year, and discontinuing Ivy Bridge. Meaning, 2 years from now most likely if you want to upgrade your CPU, you'll be buying a new motherboard.
Having said all that, most likely with a 7870 card, you'll have a good 3 or 4 years of great gameability whether you buy an overclockable CPU or not. Its your call, but honestly, I like I said, nice thing about the K CPUs is it keeps your options open.