Theoretically there is no limitation on the number of pages or templates you could use. We know about projects using 20.000 pages or 90.000+ cms users. In terms of numbers, the highest number of news articles we know so far is about 50.000.
The biggest challenge will be with the navigation controls and the page tree view in the admin section. If your pages are organized well in the page view tree you maybe able to succeed. In any case, you should consider the caching as performance factor.
You could use our APIs to high number of test content items, and see the behavior.
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