Finder copies files in two steps and does it as a transaction
From many years of experience* with transferring sets of many hundreds of thousands of files (with tens of thousands of nested folders,) the safest and quickest methods avoid the Finder completely and uses the console commands.

Don't beat your head against the wall - Finder just won't do it satisfactorily. Investigate rsync as a possible method for transfer.

*manual backups of FirstClass PostOffice directories.