Throw this in spec/support and run specs as normal. Stackprof will output a profile to the tmp directory.

capybara_profile.rb

Capybara.app =  Rack::Builder.new do
  map "/" do
    use StackProf::Middleware,
      enabled: true,
      mode: :wall,
      interval: 100,
      save_at_exit: true
    run Rails.application
  end
end.to_app