Tim Hunt wrote "[Save as new activity] - this always takes you back to the course page" - hmm, it doesn't seem so unambiguous. When creating several similar activities you may just want to return to the activity you are started from and press "update" again, because course page in editing mode is notoriously slow to download, especially with AJAX on. So it may too take you back to where you came from.
Other options seems good.
I also think now that more appropriate button title would be "Create new activity" - to say that we don't copy all content of activity, but just use it settings to create new.