You can review this site
, which was released recently. Also you could take a look the recently added sites within Sitefinity's showcases
As you know best, site performance depends of many factors like the used hosting and the type of the served content. Will be best if you could provide us more details about your future project, so we will be able to assist you with the performing of some specific performance tests, in order to verify that Sitefinity is suitable for your business needs. In general one could create Sitefinity based site with hundreds(or thousands) of pages and unlimited amount of categories/tags and this shall not lead to any performance issues.
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the Telerik team
Do you want to have your say in the Sitefinity development roadmap? Do you want to know when a feature you requested is added or when a bug fixed? Explore the Telerik Public Issue Tracking
system and vote to affect the priority of the items