I agree It isn't 24% better with regard to maximum frame rates, but it might be worth the extra fifty notes to someone for other reasons such as better performance when AA is applied, better minimum and average fps, game dependent of course. Someone else might prefer the AMD card for a completely different reason to frame rates, e.g. power draw, - something that AMD seem to have a higher priority for, and something I wish nVidia would / catch up or improve on.
Based on the graphs posted by tommybhoy the HD 6950 has higher minimum, maximum and average frame rates in the BF3 beta.
And BF3 is what this thread's about.