We shouldn't compare x-axis from the top and the bottom. However, it is interesting to see that speedups are generally better for a large variety of workloads for asymmetric architectures compared to symmetric architectures.
It is interesting to observe that even for the highly parallel red line in the bottom right graph adding a single "fat" core does increase speedup. This is likely due to the fact that a small amount of serialism is much more apparent (and speedup bounding) once the remaining parallelism is split over a large number of processors. I suspect f=0.99999 would again have a similar shape to the red line in the bottom left graph.
@apadwekar. Great comment.