I see your difficulty! I went to those web pages and tried to quickly figure out what the main differences are. There are too many models with seemingly minor/trivial differences. And these differences are not explained. Further complicating the issue is inconsistent layout of the web page. Their product line is not well differentiated.
Why not call WD themselves and get a specific answer? If they can’t give it then I’d look at another product; one where know exactly what you’re getting.