I think the one thing missing in this discussion is that although when used for the correct purposes CLR integration will prove addition to sql server it still falls foul of the same performance hit that you get with xprocs.

This is because the UMS's in sql server works in a non-preemptive mode i.e. it is a co-operative scheduler and the functions to yield are not available to external applications that is if you could trust them to yield when they should so to schedule a CLR assembly sql passes the thread to to the windows scheduler so that it can be scheduled pre-emptively and then starts up a new thread to handle the work of the sscheduler object from which the thread was taken.

This all involves context and keranl switching it's even worse if it then needs to acces the oDS layer as this involves more context switching etc.

Regards

David