I had 2 HD4870s die on me. The last one actually OC'd to 900 Mhz core. When the second one died I went back to Nvidia too 192 shader GTX 260. Overclocked to 756core, 1566 shader and 1242 ram. The GTX 260 SMOKES the hd4870 @ 900. Sorry boys but from someone with first hand experience the GTX 260 is a killer card, great overclocker. The HD4870 512MB I had were never smooth with AA on @ 1680, at the time there weren't any 1GB versions. I've never looked back.
You will enjoy your GTX 260 much more, trust me