Scaling PHP Book: I will teach you to scale PHP to millions of users 14 years ago
"Don't use ORMs"? I'm sorry, that's just plain wrong, or you were exposed to the wrong ORMs. Doctrine2 has great scalability - it has all sorts of caching built into it - result caching, query caching, and so on and so forth. It's actually -way- more scalable, and easier to develop for, than writing raw SQL (which, by the way, is a portability nightmare). Also, if you want to use a decent MVC framework, not using an ORM would be quite dumb. And if you're not using a good, modern, scalable MVC framework in this day and age, well, I pray for your soul.
So, USE AN ORM!!!