With a 3570K & a 7850 or better it will last a long time anyway, but if your next upgrade is a new PC I suggest getting a 7950 or better even if it means a cheaper CPU. But a 3570K with a board than supports xfire & SLi means you can double up on the GPU you buy in a year and it will last much longer.
I personally went with a 3570k, which was either that or a 3470, which damn near every advice topic recommended me buying. Reviews are phenomenal for the 3570k. Seems to be a beast. So yeah, good choice if that's what you're getting.
Looking at reviews on cards myself when planning my build, I ended up with the Sapphire 7870 XT (uses the tahiti chip, instead of pitcairn, and does make a difference)
GTX 660 ti vs. Sapphire 7870 XT proved to be a close match when overclocked on both running the same hardware. Sapphire edged it out in some areas, and vice versa on the 660 side.
When not overclocked, the 7870 destroyed the GTX 660 ti.
The 7870 is a cheaper card also. If you go with the sapphire version, the nice thing is the cards are quiet, and cool. They also have dual fans built into the card. Good for OC'ing.