There are a million reasons why copying/moving files will be slow.  Much depends on the drive and connection.  I do a lot of this at work with very large image and video databases.  I've found that this little tool makes the process goof-proof and much more stable

http://codesector.com/teracopy.

The free version works extremelly well.  Windows native file manager will lock and hang without giving any indication that something's wrong.  With Teracopy I can set a huge file backup to run overnight and know that it'll work.