If I'm not mistaken, ATI has announced that their new 3D chip is not due before the spring next year.

The 9800Pro will be their top product until then, and it will do quite nicely. I would be very surprised if that card wouldn't be up to running Doom3 smoothly.
Because chances are that, if Doom3 is due next winter like you say, the 9800Pro will STILL be the fastest 3D card on the planet.

nVidia will probably have a card with (more or less) equal performance as the 9800Pro by then, but I doubt they are going to have something that performs (much) better.