I'm pretty sure there will also be a HD4770 (@700mhz) that performs on par with the HD4850 and will replace it asap for $119. It's so much cheaper to manufacture so it's a given.
Those 4870 & 4850 pricecuts are insane by the way. There's no way Nvidia can counter those without severe losses. Selling 576mm2 chips for ~$150 to compete with the 4870 would be suicide.







