I bought a bag of Guatemala/Colombia/Ethiopia blend after having single origin Peru beans (all Arabica), and was struck by the difference in bean size: Peruvian beans were almost twice larger than the beans in the blend.
Now I'm wondering whether the difference is conditioned by some environmental factors, or regional differences of the coffee plant, or the timing of harvesting. Of course, it can also be that any coffee plant anywhere produces beans of (significantly) different size, and then they are sorted into size-consistent batches (as per this guide, for instance).