You will be disappointed by the performance of most of the current 3-D cards. It is unlikely that they will supply a significantly greater polygon throughput rate than unaccelerated hardware. This situation is changing quickly though, with a combination of market forces, design experience, and increasing hardware expertise.
You should be skeptical of published performance figures. They are typically peak rates, produced in ideal conditions for the renderer, and are not actually reproducible in a real-world application.
In the meantime, even if the performance is not what you might desire, many of the current hardware accelerators are still useful. For example, they typically fill polygons very quickly, particularly big polygons. The resolution of your image, the color depth at which you can run, and some special effects might also improve.