It's believable. Usually albums that open to strong #s are #1 and #1 on iTunes and #1 on Amazon. She's #1 on iTunes but the 2nd version is pretty low, and she's like #25 on Amazon.
It might. 6 million worldwide isn't an easy feat these days. I'm not entirely sure if Rihanna can do it again with this album, no matter how good it is.