Also, I now realize that I am replying to a comment from two years ago, so perhaps the realities have changed and Lumen only recently surpassed Slim in terms of performance. I'd be interested in knowing if your opinions have changed at all though.
For my work I mostly develop in Rails, but for my own projects I often use Laravel for things that need a full-stack framework, or Lumen if I don't need as much simply because it is quite performant and uses the Laravel syntax I am already so familiar with.