ergophobe - 4:22 pm on Aug 8, 2012 (gmt 0)
JB - you keep mentioning the number of pages. If it's a simple query (which a cached page in Wordpress or Drupal should be), then 100,000 pages is a *small* number, especially if you have your DB tables properly indexed and you measure and slow queries (if possible on your hosting setup).
The number of concurrent users is a far more important number and that's where the overhead of something that is highly dynamic starts to hurt. For example, the "who's online" feature of bulletin boards and forums tends to cause huge overhead in and of itself if there's a large user base.
So when you say Magento is slow, that is not likely because you have 10 pages, 10,000 pages or a million pages. It is most likely simply because generating any page in Magento takes many queries or a few very slow queries. That's the part that will make scaling difficult.
So like bhartzer says - if you use WP and implement agressive caching (WP SuperCache for example) or Drupal (with Boost), your bottleneck will likely be on the front end - CSS and JS cruft. Then it's a matter of a theme that keeps things simple, and not adding features that add complex and slow DB queries.