Performance: A php file in MU plugin folder vs. code snippet vs. actuall plugin

I just wonder if there has been any body tested performance issues on following three options:

1. Regular plugin
2. Code snippet
3. A php file in MU plugin folder

Guess it really depends on an author writes his/her plugin, but just want to have any technical expertise view on this issue.

Since all my tries with #3 were only a single PHP file, I feel that #3 affects the least in terms of performance. What about #2 vs. #3? As far as I remember, the initiative for Performant Translations – WordPress plugin | WordPress.org this plugin was that PHP files perform the fastest on PHP. Does this mean #3 w/ a simple PHP is faster than #2?

Regarding above matter, will it significantly improve website performance, if I convert most plugins to simple PHP files and run OPcache on the server?

The difference should be marginal, but just want to know if there is any margin that I can improve my website’s performance.