I recently had this problem and solved it with finddupe (http://www.sentex.net/~mwandel/finddupe/). It's a free command line tool. It can create hardlinks, you can tell it which is a master directory to keep and which directories to delete, and it can create a batch file to do actually do the deletion if you don't trust it or just want to see what it will do. Highly recommend. In any case, 5 TB is going to take forever but with finddupe you can be sure your time is not wasted, unlike one of the free tools that analyzed my drive for 12 hours and then told me it would only fix ten duplicates.
I tried this vs. Clone Spy, Fast Duplicate File Finder, Easy Duplicate File Finder, and the GPL Duplicate Files Finder (crashy). (Side note: Get some creativity guys). There's no UI but I don't care. It doesn't keep any state between runs so run it a few times on subdirectories to make sure you know what it's doing first then let it rip.