Facebook built their own PHP-to-C++ compiler (https://en.wikipedia.org/wiki/HipHop_for_PHP) and later a JIT compiler/VM (https://en.wikipedia.org/wiki/HipHop_Virtual_Machine), with a custom, typed version of PHP (https://en.wikipedia.org/wiki/Hack_(programming_language) ).

All just to make PHP a little faster. I think you are making my case.

HH transpilation was introduced in 2010. Depending on when exactly you look in 2010, FB had between 350-600M active users (https://www.yahoo.com/news/number-active-users-facebook-over...).

Many websites don't ever get to 350M users, so it's safe to say that plain PHP will satisfy your startup for a long time. Also, PHP7 is pretty much on par with HHVM in real-world scenarios: https://kinsta.com/blog/the-definitive-php-7-final-version-h...

Check out "experimental JIT branch" of PHP. It boost performance 1.5-2 times compared to current PHP 7.1, and they didn't start optimization yet. It blows HHVM out of the water, and I can't wait to compare performance with Java and .NET.

And the vast majority of websites never get 5000 concurrent users either. Your planned load obviously dictates the language as much as anything else.

PHP performs better than Java? Care to offer evidence?

Can't disclose much in public, but our PHP CMS hosting requirements tend to be waaaay cheaper than our Java-based CMSes. Also, deployment of PHP apps is (in my experience) faster and easier.

(cheaper hosting || faster deployment) != better performance