Much of this depends on whether an app has true linearity in scale-out. If you can use horizontal scalability, you can get the same (or better) aggregate performance while, as you note, still reap savings both in power and dollars. Similar by analogy to how SSDs allowed you to get "good enough" performance for a database compared to all-RAM instances. You could still meet your SLAs and pocket the difference. It's a game changer in that way.