After level 5 further career growth becomes quite challenging. The opinion of the engineering staff at Google that it's easier to leave the company and come back a level higher, than to progress while you're on your job. Another well known fact at Google that systems are very complex hindering the productivity of an IC, and there is very little effort to correct that. Software product that would take me a few month to complete at a robust company will run up to a year or more at Google, despite all the brilliant talent.