No official information has been released about which cards are the rarest, but it seems the holographic cards are a little bit harder to track down
I took out the following cards to make these upgrades: Generous Gift Rishkars Expertise Chandras Ignition Rhythm of the Wild Rampaging Brontodonb Bellowing Aegisaur Majestic Heliopterus Return of the Wildspeaker Temple Altisaur You can find the decklist here
2600 attack lets it run over most other 6 star or less monsters, most notably the Monarchs
This leaves prerelease weekend as the only possible time to do the article, and while no time is perfect, since prices are so volatile during release periods, prerelease weekend does have some benefits
BPhillipYork: Yeah okay eagles
For the former, being able to use your opponents monsters as a resource is one of the more devastating capabilities a Yu-Gi-Oh