After lots of use cases with Kirby I can say that bottlenecks happen when you put a lot (like a couple hundred or even more than thousand) subpages in a single folder. That is when scanning the list of folders gets messy. Other than that Kirby can handle A LOT of content if it’s structured more tree-ish. My biggest client website has a couple thousand subpages in a rather wide-spread tree structure and it runs extremely smooth. No page has more than 200-300 subpages and so I couldn’t find a single bottleneck even with this massive structure and more than 4 GB or files. You can check it out here: http://nimbus-lighting.com
On the other hand I had some performance issues that clearly came from servers. Some hosting providers have terribly slow disks or use some self-made “cloud” storage, which slows down Kirby more than necessary. I’m looking at Media Temples Grid system here as an example. A client went from the Grid system to Webfaction and the response times went down from 400-500ms to less than 100ms avg.
With more and more hosting providers - even the cheap ones - switching to SSD I’m quite optimistic for even better environments for file-based systems like Kirby.
Do you have any negative experiences performance-wise?