When you are after rapid turn-around of proofs then for us in Europe we must use the fastest business shipping offered. So far we have been ordering 2 books per proof. Createspace provide 2 day service for about 32 dollars (for two copies ) or 43 dollars for 4 books (2 copies from two different books).
You can combine book orders so ideally you would be pipe-lining drafts with a final proof of one book being ordered with the first proof of the next book.
This workflow is an added cost of working with Createspace in the US but it isn’t going to change until there are equivalent featured Print-On-demand (POD) providers in Europe.