If you load a bunch of packages at startup that take several seconds to load that is as good a benchmark as any. I have this at the end of my init.el:

    (run-with-idle-timer
     3 nil
     (lambda ()
       (let ((inhibit-message t))
         (message "Emacs ready in %s with %d garbage collections."
                  (format "%.2f seconds"
                          (float-time
                           (time-subtract after-init-time before-init-time)))
                  gcs-done))))