Is Craft suitable for large websites? We're looking at various CMSs for our large 11,000+ page website. We'd like to use a CMS that is appropriate for sites of that size and that will give us room to grow without impacting site speed, page load time, etc. I see other questions on this forum regarding site size, but all use CraftCMS terminology, such as 'channels', 'structures', etc to describe size.
How can CraftCMS size capability be described in pages?

Thank you.
Yes, absolutely. Craft have some case studies which illustrate that top brands trust them to handle large amounts of content while making it easy to publish more: https://craftcms.com/news/case-studies

My second point is a huge selling point for a good CMS. If your publishing process is difficult or confusing then you as an admin/client become frustrated. Craft is fast and easy to digest from a publishers point of view. 

(Wes mentioned relationships)
By design, you should only need to add a piece of content to your CMS once - and then 'relate' different entries together as new ones are published. e.g. A new 'Service' (entry) is related to an 'office location' (entry) where that service is provided.  Then, when a visitor is viewing that office location they are able to see any services which may be available there. (Just a simplified example)

Planning and designing what your content-types consist of and how different types of content can work together to tell a story to a visitor - will mitigate any major shifts in direction which often happen on-the-fly (the most expensive way to build a website). 

Coming back to your question. 
Craft is very good at storing your content efficiently. 

Craft uses Twig as a template language, which requests content from Craft. The trick is to only tell Twig to get what you need for any given page. This isn't hard once you understand the approach. 

Images are also uploaded once and then re-saved (image transforms) into different sizes as they are used differently through your site. 

The effect is that instead of slowly trying to load an image which is large in size, a small image is loaded quickly. 

Hope that helps. I'm sure you'll get more answers too...