The performance depends on how much pages are on a single level and how many nodes will be shown on the public side or the place where you want to improve page performance. Considering showing
10 000 pages would cause some issue on the public page if you do not use client side binding and load on demand, page caching and increased caching expiration is also essential for improving performance ( caching is enabled by default in Sitefinity 4.1. ).
IIS configuration is also important as mentioned here
We are currently in a process of creating a generator allowing us to test different scenarios in Sitefinity in order to provide valid statistics for the performance of Sitefinity in different situations which will give very good numerical answer to your question. We will run the tests on the frontend and backend so we will get more descriptive results. We are also working to improve the performance of the navigation widget and the sitemap widget which will be available in Sitefinity 4.2. and the optimizations that we are going to make will ensure that the out of the box navigation control will be able to work with large sitemap.
We are currently not able to provide you specifically how many pages will produce a certain load on the performance until we complete the generator that will allow us to test and get that statistical information.
All the best,
the Telerik team
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