Thanks for your comments.
1. Is `#max` defined on ActiveRecord? I get `NoMethodError` when I try it in the console. Can't find it in the documentation either.
2. We need to include `count` because it will change when a model is deleted (which `MAX(updated_at)` will not).
So I can't really see how it can be optimized further. (Be happy to more input from you and others).