would python being 3x faster make a difference? you'd still have so call out to an actually fast language when you want your code to be fast.
That is way easier to digest than the current ~5x performance penalty for using it.
I would probably not consider PHP anymore if Python was 50% of its speed.
I would never consider anything else than Python or PHP for web projects. Developer time is more precious than CPU time.
1. Maintain existing PHP codebase
2. Your team only knows PHP
You throw some PHP files on a server and have a working web application. As soon as you change a PHP file, the change is in effect on next reload of the page. You might be able to do the same in Python, but everybody in Python world is doing the long running thread approach, so you would be on uncharted territory.