Irrelevant. It isn't a valid way to compare anything as the performance difference depends more on the application and implementation. With the Phenom IIs and Athlon IIs tom's did a test to see how much of a difference cache made, in certain circumstances the Athlon's lack of an L3 cache cost it 5-10%, in other cases it made no difference at all.
If you are comparing between families don't even look at the specs, they are not comparable.
Cache can also never become a bottleneck simply by the definition of the word bottleneck. It is still part of the CPU and therefore cannot bottleneck itself, that is just called underperforming.