We now have a choice of brands of XQD cards to purchase for the D4.
Up until now, we've only had Sony, but Lexar is now shipping their XQD cards...but they sure aren't cheap.
Right now the Lexar Professional 1100x XQD Cards (32GB and 64GB) are only available through Lexar directly. B&H, Adorama, and other stores are not yet carrying these cards. I'm sure that will end soon, but I have no idea when.
The new Sony S series XQD cards are supposed to have a 168MB/s write/read speed, as is the new Lexar Professional 1100x XQD cards.
Here are the prices. I'll bet you're sticking with Sony at this point.
Sony Series S 32GB - $229 (B&H) Sony Series S 64GB - $327.55 (B&H) Lexar Professional 1100x 32GB - $449.99 (Lexar online store) Lexar Professional 1100x 64GB - $749.99 (Lexar online store)
At those prices I don't see why anyone will purchase the Lexar Cards.