Yes, Regice is worth your while. You can get only Regigigas with the Regi-trio, says common knowledge. While you wait for the opportunity, you can catch the rest of the Legendaries, given if you didn't catch them already.
Unfortunately, I currently do not have White 2 to give you the Iceberg key. This is the far as I can tell you at this moment. If you have any questions, I am more than willing to reply.