Copying one texture shouldn't cause an instant drop from 1000fps to 80, when copying 50 only drops the framerate by maybe another 2fps.
Hmm, i don't think you have read the results properly.
My tests are ALL based on 50 copies. I don't do a test for just the one copy, so i have no idea what the framerate is for that. Pretty dam fast i'd imagine.
And you don't need to lock the buffer to copyrect. It doesn't for me give much of an improvement.