My preferred way: 1. launch your site 2. wait until it starts to bog under load 3. add caching in the bogged down areas so you can still make money 4.

My preferred way: 1. launch your site 2. wait until it starts to bog under load 3. add caching in the bogged down areas so you can still make money 4. use the time you just gave yourself to optimize 5. Repeat 2-4 Adding caching should be as quick as finding the bottle neck. Sure optimizing might take you the same time but it might be a critical flaw that you're better off caching around until you have time for a refactor. Either way your customers are happy while you toil away in the code.