I would like to test the performance of PHP files in my installation, to find any bottlenecks. I already use plugins like Debug Queries and WPDB Profiler to watch the SQL Queries being generated, but I would like something that shows me the execution time of each php file to identify if some plugin is not optimised. Is there any plugin for this?
No. And even if there was, it would be probably useless anyway.
You would get incorrect results, because a .php file might call slow functions from WordPress core files, and there are a lot of situations like this.
You could try using the xdebug extension, it's pretty close to what you're looking for