Do you plan to crossfire? The new 6k series usually scales better under crossfire, which actually makes them equal to or better than the old series. Even if you don't, drivers haven't totally matured for these cards yet, although they are similar to the old gen, they aren't exactly the same(especially since 1120 shaders can now beat 1440 shaders, 6870vs5850).
The GTX 470 generally equals or beats the 6870 though(except when two cards are present), so it would also be a good deal.
When tessellation becomes more popular the GTX 470 will also scale better under higher tessellation factors, this will make the GTX 470 a better choice later down the road if it can still play games with its better tessellation scaling anyway