Marketing material from AMD suggests the upcoming Radeon HD 4830 graphics card will be 10-25% faster than a GeForce 9800 GT, on average.
AMD has already started projecting the HD 4830 to outperform the the G92GT, in essence, the GeForce 9800 GT. In a slide titled "Best Graphics Card for <$150", the company puts up figures where the new card is projected 10% faster in most games tested. The only glitch, is that most of AMD's own increment projections are based around that 10% mark, which means it could be a very tight contest between the HD 4830 and 9800 GT. A prelude could be that for the 9800 GT, its CUDA and PhysX processing capabilities could bail it out, if it does fall into a tight spot, as in, if the two end up in a neck and neck contest. The new Radeon accelerator comes out sometime next month.