ergophobe - 4:56 am on Aug 7, 2012 (gmt 0)
The number of pages on a site is perhaps the least important factor in choosing a way to manage that content.
Any CMS can handle that though if I recall correctly, traditionally WordPress has performance issues with large numbers of "pages" (but not large number of "posts"). Sometime like that.
Anyway, what's really going to matter is how the pages are put together (how many DB tables are you drawing from, are they indexed, can the queries and/or pages be cached and so on), how many concurrent users you have at *peak* load, and what you have for hardware ($30/mo can get you a decent VPS if you don't need a lot of support) and software (opcode caching or not) etc.
If I were expecting a lot of users and complex or numerous DB queries, I would want to be sure the system had good caching. This might be simple or complex. On some sites, I've just grabbed the output buffer in PHP and if there's no static version of the page, cache one. On the next request, you're serving static pages with just a quick check for whether not the cached version exists.
If you don't have a lot of dynamic content, you can get very fast page loads even if the initial page generation is processor/memory intensive.