I will wait for official reviews, but if these numbers are true than it would be consistent with the loss of stuff like ROPs or texture units.
That was what makes the 5830 such a disappointing card - half rops compared to the 5850 and less 16 texture units - I remember reading something that the GTX 460 could have the same problem.
The total number of texture units is not as important as the number of shader units, with the RATIO of texture to shader units taken into account. A GPU with a ton of texture units but few shader units is going to be dog slow. A GPU with a ton of shader units will be bottlenecked by few texture units, but will be better than the first GPU.
5830 loses 16 texture units compared to 5850, but the ratio doesn't change, and the 5830 is clocked higher. The performance loss from 16 fewer texture units and 320 fewer shaders is only about 10%.
I think everyone's opinions will differ, but I would rather cut ROPs than shader and texture units. Of course the 5830 loses all of those compared to the 5850/5870, but it takes a disproportionately large reduction in ROPs.
Losing ROPs just means performance in old games at high resolution and high AA settings won't be that great. The affect on newer games will be smaller since shader and texture limitations would come into play before ROPs. I think that's a fair sacrifice.