The R420 chip from ATis was taped out the last days of December 2003 just like NVIDIA his NV40 chipset. One difference is that ATi will be able to send samples to manufactureres right now, and that NVIDIA will problably wait until the end of February.
This means that ATI could have a one month lead in development, with the whole supply chain preparing to make printed circuit boards using the R420.
While ATI's most recent silicon isn't as fast as the A2 silicon that comes later, it is apparently good enough to finish designing the graphics chip into boards.
Both ATI and Nvidia are expected to launch the chips at this year's CeBIT show, while they will both just have a few working cards. The cards using the new graphics technology is likely to become available in shops in April/May.
It's simply too early to say what chip frequencies these new introductions will have.
But one thing is already clear. ATI and Nvidia will be fighting hammer and tongs over technologies which are spookily similar in specification and functions.