Thank's.��
I try tests for subscribing and what I found is:
Main problem that subscriptions inside SubscriptionRegistry are managed as IdentitySet which of cause much slower for addition then OrderedCollection. We probably could use OrderedCollection here because items are always created on fly and identitySet has no sense.
Another problem is access protection by mutex (semaphore) which make it 3 times slower.��
So with OrderedCollection and disabled mutex performance for subscribing is same.
I pretty sure that protection is required for Block handlers too.��