If you are worried about performance because it nags at you and not because you have a specific known performance pain, I would suggest selecting a higher-performance platform and framework so that you can defer scale concerns until much later. With a high-performance framework, you can build your application with the peace-of-mind that performance won't be a problem unless your product has decent market traction.

A common problem I've observed several times with low-performance frameworks is that you can run into performance pain before you've adequately vetted your project's ability to convert customers. By comparison, a high-performance framework allows you to be experimental and relatively reckless with your application logic. Your application code can be closer to brute-force with a high-performance platform, meaning you can optimize the application code later when the time comes, rather than bringing out the big guns of scalability.