Will a plain PHP website be faster than WordPress (if PHP code is same)?

You might find this to be helpful…

https://wp2static.com/

When implemented properly you can use that plugin to run WordPress as the backend to your website then you’ll use the generated static pages for the site itself.

Caveats are you’ll lose the interactive bits like comments and any store cart system will need to be separate but Leon covers that very well with the documentation.

Speed depends on coding practices,
WordPress is a established framework and CMS,
your “plain PHP” will likely be maintained by less people, it will have less extensibility and higher risk to become an abandonware.

It may be faster, a bit, because you will likely not be using a lot of features,
but the bottlenecks will be same – MySQL, disk IO.

If you are looking to build a really fast site using PHP, look at PHP Phalcon
this is a framework presented as PHP extension (written in C, and therefore it is very fast, but you will need VPS or dedicated or otherwise managed by yourself server).

Using WordPress will save you time, efforts and money. WP performance is still good on a good hosting. The choice is yours.

Faster to write or faster to load ?

@rossmitchell which one will be faster to load (If PHP code is same)?
Thanks.

Well if the php is the same, then both would be WordPress sites.

Truly with fast enough hosting, then the ease of use of WordPress makes it a non contest, just my opinion.