Eliot wrote:

About 90% of the entire time is in the string copying primitive. Not much to be done there. Sista could speed this up by eliminating the validation overhead of the primitive. But with our current VM technology there's not a lot one can do given that OrderedCollection is organized as a flat stack. This is probably a case where an ordered tree would be faster, albeit have a lot more space overhead.

Switching collections backing store to a chunked representation once they grow beyond a certain threshold is probably the best thing to support larger collections. Stephan