Well, about recycle app pool i have contacted to provider and they give me this info
Windows Server 2008/IIS 7:
* Idle timeout set to 20 minutes. (Information is NOT logged)
* Memory threshold set to 200 MB.
* CPU limit set to 70% utilization over 300 seconds (5 minutes).
So it seems that recycle app pool was by idle timeout.
About extensions - i have change code for now in ExtensionManager that it will use
Dictionary<string, ManagedExtension> extensions
instead of and add comechecking when Extension is adding to dictionary.
In dictionary string key is the name of the extension, so there is more space to optimize places where extensions are getting from the dictionary by key. Dictionary is based on HashTable so it could work faster i think. Will see how it will run couple next
days. Also did all changes to lists of extension in admin section. Ben if you will be interesting i could send code to you.